Transmembrane signaling in arbuscular mycorrhizal symbiosis

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Leng et al. reveal a pathway regulating arbuscule development in plant symbiosis with arbuscular mycorrhizal fungi. The Plant Cell (2023).

By Marcel Bucher (University of Cologne) and Li Xue (Zhejiang Normal University)

Background: More than 80% of terrestrial plants form mutualistic symbiosis with arbuscular mycorrhizal (AM) fungi. Arbuscules, the branching hyphae inside the plant cell, are characteristic of AM symbiosis and facilitate nutrient exchange between host and fungi. Arbuscule development is tightly controlled in host cells. Kinases play a central role in cell signaling processes, but the function of AM-induced kinases (AMKs) in arbuscule formation is still largely unknown.

Question: We were interested in identifying AMKs that regulate arbuscule development and deciphering the underlying molecular mechanism.

Findings: Our phylogenetic analysis revealed that nine AMKs are AM-host specific. Among them, the receptor-like kinase KINASE3 (KIN3) and the receptor-like cytoplasmic kinases AMK8 and AMK24 are required for AM symbiosis in Lotus japonicus and are transcriptionally regulated by the transcription factor CTTC MOTIF-BINDING TRANSCRIPTION FACTOR1 (CBX1). AMK8 and AMK24 interact with KIN3 at the cellular membrane. KIN3 and AMK24 are active kinases and AMK24 phosphorylates KIN3. Moreover, the AMK8 and AMK24 homolog in rice is indispensable for AM symbiosis. Our results highlight the critical role of the KIN3-AMK8/24 complex in AM symbiosis and suggest a pathway across the periarbuscular membrane that controls arbuscule development.

Next steps: We plan to identify interacting proteins of the KIN3-AMK8/AMK24 complex that mediate downstream AM signaling, as well as the potential fungal or plant signals that the complex senses.

Reference: 

Junchen Leng, Xiaotong Wei, Xinyi Jin, Longxiang Wang, Kai Fan, Ke Zou, Zichao Zheng, Georgios Saridis, Ningkang Zhao, Dan Zhou, Deqiang Duanmu, Ertao Wang, Haitao Cui, Marcel Bucher and Li Xue (2023). ARBUSCULAR MYCORRHIZA-INDUCED KINASES AMK8 and AMK24 associate with the receptor-like kinase KINASE3 to regulate arbuscular mycorrhizal symbiosis in Lotus japonicus. https://doi.org/10.1093/plcell/koad050

Developing a System of Accountability at Plant Conferences

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Personal safety and freedom from harassment & discrimination at conferences have been identified as major concerns, particularly amongst people who experience significant intersections of oppression. Furthermore, clear systems of accountability are needed to address occurrences of harm. As first steps, The NSF-funded ROOT & SHOOT Research Coordination Network has arranged for onsite Conference Ombuds services at three 2023 summer plant conferences, and is beginning to work towards systems of accountability based on principles of restorative justice.

Small RNAs and nutrient deprivation in Chlamydomonas

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Li et al. find a class of small RNAs that might affect algal tolerance to nutritional stress.

 Yingshan Li and Heriberto Cerutti – School of Biological Sciences and Center for Plant Science Innovation, University of Nebraska-Lincoln, NE 68588-0666, USA

 Background: Noncoding RNAs are not translated into proteins. However, many play key roles in various biological processes. In eukaryotes, small RNAs can bind to matching messenger RNAs (mRNAs) and trigger their degradation or shut down their translation into proteins, a phenomenon called RNA interference. These small RNAs associate with Argonaute (AGO) proteins and regulate the expression of protein-coding genes. Other kinds of small RNAs help fight viruses and transposons. Generally, all these types of small RNAs are produced by cleaving longer double-stranded RNAs via Dicer ribonucleases. Indeed, in many organisms, diverse Dicer-dependent small RNAs affect growth, development and disease tolerance.

Question: We wanted to characterize the small RNAs functioning in the single-cell alga Chlamydomonas reinhardtii. This green alga lives in many different environments throughout the world and has become a valuable model for biological research.

Findings: Chlamydomonas reinhardtii contains a class of small RNAs (greater than 26 nucleotides in length) that associates preferentially with a specific Argonaute protein named AGO1. These small RNAs are atypical since they do not require Dicer enzymes for their production. They are derived from moderately repetitive, transposon-like sequences conserved in related Chlamydomonas species. Interestingly, the abundance of these small RNAs increased substantially in cells subject to nitrogen or sulfur deprivation, simultaneously with the downregulation of predicted target mRNAs. We postulate that this class of small RNAs might have a role in algal tolerance to nutritional stress.

Next steps: We would like to find out how these small RNAs may help the alga cope with nitrogen or sulfur deprivation and the molecular mechanism(s) by which they may regulate gene expression. This information may be helpful for improving nutrient use efficiency in crops.

Reference: 

Yingshan Li, Eun-Jeong Kim, Adam Voshall, Etsuko N. Moriyama, and Heriberto Cerutti (2023) Small RNAs >26 nt in length associate with AGO1 and are upregulated by nutrient deprivation in the alga Chlamydomonas. https://doi.org/10.1093/plcell/koad093

Magnaporthe oryzae cytoplasmic effector translocation via endocytosis

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Oliveira-Garcia et al. investigated Magnaporthe oryzae effector internalization inside rice cells. The Plant Cell (2023)

By Ely Oliveira-Garcia, Nicholas J. Talbot and Barbara Valent

Background: To cause disease in plants, fungal pathogens deliver effector proteins directly into plant cells. Inside the host, effectors suppress the plant immune system and enable pathogens to rapidly invade and proliferate within plant tissue. How effector proteins enter plant cells, however, is not understood. During plant infection, the devastating rice blast fungus forms a specialized interfacial region known as the biotrophic interfacial complex (BIC), which is necessary for effector delivery into plant cells. We set out to explore how the BIC fulfils this role and how effectors enter plant cells.

Question: How does the blast fungus deliver effector proteins across the plasma membrane into living rice cells?  Does the effector delivery system involve endocytosis by plant cells?

Findings: Live cell imaging of the blast fungus growing in rice cells, provides evidence that effector proteins are packaged in dynamic vesicle-like membranous effector compartments (MECs) at the BIC. These MECs are bounded by the rice plasma membrane and clathrin light chain-1. Inhibition of endocytosis by chemical treatment or silencing rice genes involved in clathrin-mediated endocytosis prevent MEC formation and pathogenicity. An effector, Bas83, appears to play a role in recruiting regions of the plant membrane for endocytosis to the BIC. Taken together, our results provide evidence that clathrin-mediated endocytosis is necessary for effector translocation into plant cells.

Next steps: We would like to know how clathrin-mediated endocytosis is induced by the blast fungus during plant infection. How does Bas83 recruit plant membrane to promote endocytosis, for example, and can we identify new effectors involved in co-opting host endocytosis to enable internalization of cytoplasmic effectors?

Reference:

Ely Oliveira-Garcia, Tej Man Tamang, Jungeun Park, Melinda Dalby, Magdalena Martin-Urdiroz, Clara Rodriguez Herrero, An Hong Vu, Sunghun Park, Nicholas J. Talbot & Barbara Valent (2023) Clathrin-mediated endocytosis facilitates the internalization of Magnaporthe oryzae effectors into rice cells. Plant Cell. https://doi.org/10.1093/plcell/koad094

Two isoforms of ELF3 antagonistically regulate flowering

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Wang, Li, Liu, Li et al. explore how alternative promoter usage at the ELF3 locus regulates flowering.

By Peng Wang1,2, Yu Li1,2, Zhe Liu1,3, Xuhan Li1, Shaoling Zhang1,2, Juyou Wu1,2,4

1Sanya Institute of Nanjing Agricultural University, National Key Laboratory of Crop Genetics & Germplasm Enhancement and Utilization, Nanjing Agricultural University, Nanjing, 210095, China

2College of Horticulture, Nanjing Agricultural University, Nanjing, 210095, China

3Department of Pharmacy, Changzhi Medical College, Changzhi, 046000, China

4Jiangsu Key Laboratory for Horticultural Crop Genetic Improvement, Nanjing, 210014, China

Background: Flowering is critical for sexual reproduction and fruit production. The circadian clock regulator EARLY FLOWERING3 (ELF3) serves as a scaffold protein in the evening complex that controls flowering. EARLY FLOWERING4 (ELF4) and the transcription factor LUX ARRHYTHMO (LUX) directly bind to ELF3 to form the evening complex (EC) that gates circadian clock–mediated physiological responses in multiple species. Alternative promoter usage has been identified as a critical response to environmental signals in thousands of genes. However, the function of alternative promoter usage in flowering time regulation, particularly in relation to ELF3 function, remains poorly understood.

Question: How does alternative promoter usage at the ELF3 locus regulate flowering?

 

Findings: Here we report that alternative promoter usage generates two transcript isoforms from the ELF3 locus. This phenomenon is conserved among plants such as Arabidopsis (Arabidopsis thaliana), soybean (Glycine max), tomato (Solanum lycopersicum), apple (Malus × domestica), and pear (Pyrus sp,). Our results indicate that the full-length transcript ELF3α and the shorter transcript ELF3β antagonistically regulate flower induction. The 2nd intron of the ELF3 locus is critical for ELF3β expression. We determined that the AtELF3β transcript isoform encodes a protein that promotes flowering by competitively binding to AtELF3α and thereby disrupting EC complex formation. Our findings thus establish a mechanism for fine-tuning flower induction that depends on manipulating transcript isoforms through alternative promoter usage.

Next steps: In further studies, we will investigate the detailed mechanisms by which the second intron regulates ELF3β expression and how ELF3β expression responds to the environment.

Reference:

Peng Wang, Yu Li, Zhe Liu, Xuhan Li, Yicheng Wang, Weijuan Liu, Xiao Li, Jianjian Hu, Wenyi Zhu, Changquan Wang, Shan Li, Tingting Gu, Dongqing Xu, Chao Tang, Yingtao Wang, Chao Li, Shaoling Zhang, Juyou Wu. (2023). Reciprocal regulation of flower induction by ELF3α and ELF3β generated via alternative promoter usage. https://doi.org/10.1093/plcell/koad067

 

ELF3的选择性转录调控花芽分化

最近 Wang et al.在The Plant Cell在线发表了题为Reciprocal regulation of flower induction by ELF3α and ELF3β generated via alternative promoter usage的研究论文，揭示了ELF3基因的选择性转录调控花芽分化的分子机制。

  1. 背景回顾

开花是植物有性生殖的重要过程，也是果树生产的关键环节。生物钟调控因子EARLY FLOWERING3（ELF3）作为Evening Complex的重要组分，参与花芽分化调控。EARLY FLOWERING4（ELF4）和转录因子LUX ARRHYTHMO（LUX）直接与ELF3结合形成Evening Complex，在多个物种中调控昼夜节律介导的生理反应。虽已发现多种环境信号影响可变启动子的选择性转录，但ELF3选择性转录及其在调控花芽分化中的作用尚不明确。

  1. 科学问题

ELF3基因的可变启动子如何调节花芽分化？

  1. 研究发现

本研究发现ELF3基因具有可变启动的特性，能够编码ELF3α和ELF3β两种蛋白。ELF3β与ELF3α结合形成聚合体后，抑制ELF3α-LUX转录调控复合体的功能，进而调控花芽分化。同时，在苹果、大豆、番茄和拟南芥等物种中也鉴定到ELF3β转录本，表明ELF3基因的可变启动调控机制可能广泛存在于在植物界。研究结果进一步丰富了对梨花芽分化分子调控机制的认知，为梨育种提供了可靠的分子标记。

  1. 展望未来

在进一步的研究中，我们将探究ELF3基因的第二个内含子调控ELF3β表达的机制，解析ELF3β响应环境变化的调控网络。

Huijie Liu: The Plant Cell First Author

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Huijie Liu, co-first author of “N4-acetylation of cytidine in (m)RNA plays essential roles in plants” 

Current position: Ph.D. candidate, Nanjing Agricultural University

Education: Master, Hangzhou Normal University

Non-scientific Interests: traveling and watching movies

Brief bio:

In 2022, I obtained my master’s degree from Hangzhou Normal University, and then join to Prof. Dr. Mingjia Chen’s lab at Nanjing Agricultural University where I pursue my Ph.D. study focusing on the identification and characterization of RNA modification in plants. In this project, we demonstrate the wide occurrence of cytidine N4-acetylation (ac4C) on mRNAs from various vascular plants. Using acRIP-seq, we mapped the distribution of ac4C modifications in Arabidopsis thaliana. Several lines of evidences showed that N-ACETYLTRANSFERASEs FOR CYTIDINE IN RNA 1 (ACYR1) and ACYR2 are partially redundant and together responsible for RNA acetylation in Arabidopsis. In the future, I will continue my work on the functional analysis of RNA modification in plant and strive to make some new progress in this field.

姓名：刘慧婕

发表论文：N4-acetylation of cytidine in (m)RNA plays an essential role in plants

目前职位：南京农业大学，博士生

教育经历：杭州师范大学，硕士学位

兴趣爱好：旅游，看电影

个人简历：

我于2022年在杭州师范大学获得硕士学位，同年进入南京农业大学生命科学学院陈铭佳课题组攻读博士学位，主要从事RNA新型化学修饰功能解析工作。

我们的研究证实了高等植物mRNA中广泛存在胞嘧啶乙酰化（ac4C）修饰。利用acRIP-seq，我们绘制了拟南芥叶片ac4C修饰图谱。生化和生理实验结果证明植物RNA乙酰化酶ACYR1和ACYR2部分功能冗余，共同介导全局ac4C修饰。未来，我将继续从事RNA修饰功能解析工作，努力在这一领域取得新进展。

TaGSK3 regulates the Green Revolution Protein Rht-B1b to reduce wheat plant height

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Dong, Li, et al. explore the mechanisms regulating a Green Revolution protein that acts to reduce plant height

Huixue Dong1,2,3, Danping Li1,3, Ruizhen Yang1, Lichao Zhang1, Yunwei Zhang1, Xu Liu1, Xiuying Kong1,*, and Jiaqiang Sun1,*

  1. State Key Laboratory of Crop Gene Resources and Breeding, Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, Beijing, China
  2. State Key Laboratory of Crop Gene Exploration and Utilization in Southwest China, Sichuan Agricultural University, Chengdu, Sichuan, China
  3. These authors contributed equally to this work.

*Corresponding authors.

Background: For wheat (Triticum aestivum), plant height is a crucial agronomic trait because high plants are prone to lodging (falling over). During the Green Revolution in the 1960s, the unprecedented wheat yield increases were achieved through the introduction of Reduced height (Rht)-B1b and Rht-D1b semi-dwarfing alleles, which confer increased harvest index and improved lodging resistance. Rht-B1b and Rht-D1b alleles produce N-terminal truncated DELLA proteins generated by translational re-initiation, which are stabilized by lacking an intact DELLA motif, leading to reduced plant height. The DELLA proteins are well known as negative regulators of gibberellin signaling in plants. However, the molecular basis of how the Green Revolution proteins Rht-B1b and Rht-D1b act to reduce plant height in wheat remains to be clarified.

Question: How is the stabilized Rht-B1b protein activated or regulated to reduce plant height in wheat?

Findings: We cloned a gain-of-function allele of GSK3 gene through characterization of a dwarf wheat mutant. The GSK3 kinase was shown to interact with and phosphorylate Rht-B1b to promote it to reduce wheat plant height. The phosphorylation by GSK3 may enhance the activity and stability of Rht-B1b. Moreover, GSK3-mediated plant growth repression requires DELLA proteins. Overall, we uncover an activation mechanism for the Green Revolution protein Rht-B1b, which not only needs to be stabilized but also needs to be activated by direct phosphorylation via GSK3 to exert its function in reducing wheat plant height.

Next steps: We plan to generate more wheat mutants with modified plant architecture by CRISPR/Cas9 or EMS-mutagenesis and elucidate the regulatory network of wheat plant architecture, which will provide new insights and elite genes for wheat improvement.

Reference:

Huixue Dong, Danping Li, Ruizhen Yang, Lichao Zhang, Yunwei Zhang, Xu Liu, Xiuying Kong and Jiaqiang Sun (2023) GSK3 phosphorylates and regulates the Green Revolution protein Rht-B1b to reduce plant height in wheat. Plant Cell. https://doi.org/10.1093/plcell/koad090

 

 题目：TaGSK3帮助绿色革命蛋白Rht-B1b降低小麦株高

背景回顾：株高是小麦重要的性状之一，株高太高容易出现倒伏。在20世纪60年代的“绿色革命”期间，通过引入半矮化等位基因Rht-B1b和Rht- D1b，提高了小麦收获指数和抗倒伏能力，使小麦产量获得了前所未有的提高。Rht-B1b和Rht-D1b等位基因通过重新启动转录产生N端截断的DELLA蛋白。DELLA蛋白由于缺乏完整的DELLA基序而变得稳定，导致株高降低。众所周知，DELLA蛋白是植物赤霉素信号传导的负调控因子。然而，绿色革命蛋白（Rht-B1b和Rht-D1b）如何降低小麦株高的分子基础仍不清楚。

科学问题：稳定的Rht-B1b蛋白是如何被激活或调控以降低小麦株高?

研究发现：通过分析一个小麦矮秆突变体，我们克隆到了功能获得性的TaGSK3等位基因。发现TaGSK3激酶可以与绿色革命蛋白Rht-B1b相互作用并磷酸化Rht-B1b，进而促进Rht-B1b实现降低小麦株高的生物学功能。试验分析表明TaGSK3介导的磷酸化可以增强Rht-B1b的活性和稳定性。此外，TaGSK3介导的生长抑制作用依赖于DELLA蛋白的功能。我们揭示了一个小麦绿色革命蛋白Rht-B1b的激活机制：Rht-B1b蛋白不仅需要稳定，还需要被TaGSK3激酶直接磷酸化激活，才能发挥其降低小麦株高的作用。

展望未来：我们计划通过CRISPR-Cas9或EMS诱变创制更多株型变异的小麦突变体，并阐明小麦株型的调控网络，为小麦株型改良提供新的思路和优异基因资源。

Phosphate uptake in maize

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Wang, Yuan, et al. explore the regulatory connection between phosphorus nutrient homeostasis and vegetative-reproductive development in maize.

Background: Phosphorus is an essential macronutrient for plant growth and development. To cope with phosphorus limitation, plants have evolved sophisticated strategies to coordinate phosphorus acquisition, scavenging and recycling. Maize is an important crop and cultivated widely for both staple food and industrial usage. Although phosphorus is a major constituent of the fertilizers required to sustain high yields in maize, global phosphorus resources are quickly diminishing and may be exhausted in the near future.

Question: We sought to understand the underlying molecular mechanisms behind phosphate acquisition and utilization in maize to develop varieties with high phosphorus use efficiency.

Findings: We observed that overexpressing microRNA399 (miR399) or knocking out of its target gene ZmPHO2 results in an apparent leaf senescence phenotype after pollination. We further discovered that the transcription factor INDETERMINATE1 (ID1) functions as an autonomous upstream regulator of phosphorus homeostasis by suppressing the transcription of ZmMIR399 genes, thus decreasing the accumulation of mature miR399 and alleviating the cleavage of ZmPHO2 transcripts, ultimately contributing to the maintenance of phosphorus homeostasis in maize. Our work establishes a regulatory connection between phosphorus nutrient homeostasis and vegetative-reproductive development in maize. More importantly, we show that ZmPHO2 underwent strong selection during maize domestication and cultivation. This study provides genetic resources for improving maize phosphorus use efficiency and breeding low phosphorus-tolerant maize varieties by editing the ID1-miR399-ZmPHO2 module.

Next steps: We will attempt to generate ID1-modified plants to fine-tune flowering time and phosphorus uptake in maize. The specific functions of each MIR399 family member may also be interrogated by generating genome-edited mutants. As we discovered that Bx genes involved in benzoxazinoid biosynthesis are also affected by miR399, we hope to further explore the mechanism of miR399 functioning as a negative regulator of plant immunity.

Reference:

Xufeng Wang, Dan Yuan, Yanchun Liu, Yameng Liang, Juan He, Xiaoyu Yang, Runlai Hang, Hong Jia, Beixin Mo, Feng Tian, Xuemei Chen, and Lin Liu (2023). INDETERMINATE1 autonomously regulates phosphate homeostasis upstream of the miR399-ZmPHO2 signaling module in maize. Plant Cell. https://doi.org/10.1093/plcell/koad089

 

Chinese Translation

 背景回顾：磷是植物生长发育不可缺少的元素之一。为了应对磷缺乏，植物已经进化出多种复杂的策略来协调磷酸盐的获取、清除和再利用（回收）过程。玉米是一种重要的粮食作物，如今已经在全世界范围内被广泛种植。磷是维持玉米高产所需肥料的主要成分之一，然而磷资源正在迅速减少，并可能在不久的将来枯竭。

科学问题：我们试图了解玉米磷酸盐获取和利用的潜在分子机制，以开发具有高磷酸盐利用效率的品种。

研究发现：通过实验室和大田评估，过表达玉米microRNA399家族或敲除其靶基因 ZmPHO2 会导致玉米在授粉后出现明显的叶片早衰表型。进一步研究发现，转录因子 INDETERMINATE1 (ID1) 作为上游调节因子可以有效抑制 ZmMIR399 基因的转录，从而减少成熟 miR399 的积累并减轻其对靶标基因ZmPHO2的转录切割，最终将有助于玉米体内磷稳态的维持。我们的工作试图在玉米的磷稳态和营养、生殖发育之间建立联系。更重要的是，我们发现 ZmPHO2 在玉米驯化和栽培过程中可能受到了强烈的选择。本研究在玉米中建立了ID1-miR399-ZmPHO2调控模块，为提高玉米磷酸盐利用效率和培育耐低磷玉米品种提供了宝贵的遗传资源。

展望未来：后期，我们将尝试创建不同ID1表达水平的转基因或基因编辑植物来微调玉米的开花时间和磷酸盐吸收效率。每个 miR399 家族成员的具体功能尚不清晰，我们将试图利用 CRISPR-Cas9 技术生成每个 miR399 家族成员对应的突变体来研究其功能。我们发现参与苯并恶嗪（丁布）次生代谢途径生物合成的Bx基因表达也受到miR399表达的影响，希望进一步探索miR399在植物免疫中作为负调节因子发挥作用的机制。

A new regulatory module controls chlorophyll catabolism in bananas under high temperature

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Wei et al. discover a new transcriptional and post-translational regulatory module, MaBAH1-MaMYB60, that regulates chlorophyll catabolism and green ripening in bananas under high temperature.

By Wei Wei, Yingying Yang, Prakash Lakshmanan, Jianfei Kuang, Wangjin Lu, Xuequn Pang, Jianye Chen and Wei Shan

Background: Bananas are harvested at the mature-green stage and transported to wholesale markets, where they ripen to a golden yellow peel with ethylene. Ripening at temperatures above 24 °C (e.g., 30 °C) makes fruits soften faster but its peel remains fully green. This phenomenon is called green ripening, and it is a highly undesirable and loss-making fruit quality condition for banana marketing. The current global warming makes this problem particularly significant. However, the regulatory mechanism underpinning high temperature-induced repression of chlorophyll catabolism and green ripening remains unknown.

Question: What are the crucial genes involved in high temperature-induced green ripening? What are their upstream regulators?

Findings: During the green ripening of banana fruits at 30 °C, expression of five chlorophyll catabolic genes (CCGs), MaNYC1, MaSGR1, MaSGR2, MaPPH and MaTIC55, was significantly reduced. We found that a MYB transcription factor MaMYB60, which targeted and activated the five CCGs, caused chlorophyll degradation in bananas, but its activation was weakened at 30 °C. More importantly, a RING-type E3 ligase MaBAH1 ubiquitinated and targeted it for proteasomal degradation. MaBAH1 thus facilitated MaMYB60 degradation and attenuated MaMYB60-induced trans-activation of CCGs and chlorophyll degradation. Furthermore, the MaBAH1-mediated degradation of MaMYB60 was enhanced under high temperature, which dampened MaMYB60-promoted chlorophyll degradation. Collectively, our findings unravel a new dynamic, temperature-responsive MaBAH1-MaMYB60-CCGs module that regulates chlorophyll catabolism, and the molecular mechanism underpinning green ripening in bananas.

Next steps: We will continue to discover other regulators such as post-translational protein and epigenetic modifiers, which function in modulating chlorophyll catabolism and green ripening under high temperature. These findings will reveal the multilevel regulatory mechanisms behind this phenomenon, and advance our understanding of plant responses to high-temperature stress.

Wei Wei, Ying-ying Yang, Prakash Lakshmanan, Jian-fei Kuang, Wang-jin Lu, Xue-qun Pang, Jian-ye Chen, Wei Shan. (2023). Proteasomal degradation of MaMYB60 mediated by the E3 ligase MaBAH1 causes high temperature-induced repression of chlorophyll catabolism and green ripening in banana https://doi.org/10.1093/plcell/koad030