14-3-3 Proteins Function in Plant Immunity

/in /by

Dong et al. investigate the role of 14-3-3 proteins in plant immunity in Arabidopsis.

By Xiaojing Dong and Jian-Min Zhou

Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China.

Background: The plant innate immune system detects the presence of microbial pathogens and triggers defense responses to terminate or restrict pathogen progression. The BIK1 family receptor-like cytoplasmic kinases (RLCKs) play a crucial role in immune signal transduction and regulate multiple substrate proteins. Much less is known concerning how these kinases and their substrates are organized in a way for robust signaling.

Question: We were interested in identifying interactors of RLCKs and understanding how they regulate immunity.

Findings: We found that the 14-3-3 proteins GRF6 and GRF8 play a key role in both anti-bacterial and anti-fungal immunity in Arabidopsis. We show that these 14-3-3 proteins directly interact with MAPKKK5 to enable their activation by upstream RLCKs. Our study reveals how GRF6 and GRF8 act as a scaffold to regulate the RLCK-MAPKKK5 module to facilitate the activation of MAP kinase cascades during immune signaling.

Next steps: It would be of interest to investigate whether different 14-3-3 members regulate different immune responses and how.

Reference:

Shaofei Rao, Zhaoyang Zhou, Pei Miao, Guozhi Bi, Man Hu, Ying Wu, Feng Feng, Xiaojuan Zhang, and Jian-Min Zhou (2018) Roles of receptor-like cytoplasmic Kinase VII members in pattern-triggered immune signaling. Plant Physiol.  https://doi.org/10.1104/pp.18.00486

Xiaojing Dong, Feng Feng, Yangjun Li, Lin Li, She Chen, Jian-Min Zhou. (2023) 14-3-3 proteins facilitate the activation of MAP kinase cascades by upstream immunity-related kinases. Plant Cell.  https://doi.org/10.1093/plcell/koad088

Front and Center Celebrates and Connects Black, Indigenous, and Latine Plant Scientists

/in /by

I often joke that one of the best things about working as a plant scientist is getting to be alone with my plants in the lab. In practice, I get a lot of my joy from working with other plant biologists: learning from them, mentoring folks, and discovering and celebrating all the wonderful things that plants have to teach us. Fostering strong connections with other plant scientists from different communities is essential to our success at every stage of our careers, and for the strength of the work we produce.

Fostering connections among Black, Indigenous, and Latine plant scientists helps us navigate institutions that were not designed with us in mind, and yet finding folks to connect with can be especially difficult due to a history of exclusion that often sees us as “the only one” in our labs, departments, or even institutions. To this end, Dr. Imani Madison and Dr. Edith Pierre Jerome created Front and Center, a network that celebrates and connects Black, Latine, and Indigenous plant scientists. Today, Dr. Kevin Cox and I, Dr. Román Ramos Báez, direct Front and Center with support from ASPB and NAASC. 

Front and Center Features is a social media project directed by Dr. Román Ramos Báez. Every week, we feature a self-nominated plant scientist through LinkedIn, Instagram, Twitter, and/or Threads. Submitting a feature is a great way to share your story, invite the broader community to get to know you and celebrate you, as well as help you to connect to folks with similar interests and experiences. It can also help you inspire others to pursue plant science, learn about different career paths, and make yourself visible to plant biology newcomers. Follow us on our socials to populate your social media feeds with amazing Black, Latine, and Indigenous plant scientists. You can submit a profile to be featured here.

Adventitious Roots is a Slack and Discord channel directed by Dr. Kevin Cox. It allows folks to organize with and speak directly to other members that choose to be a part of it. Consider joining our Safe Space Discord Server to seek advice, support, or a listening ear. This is also for those who have navigated these institutions and have a wealth of experience, advice, and knowledge to share with newcomers. Lastly, this is a place to vent frustrations without retribution. At the beginning of my scientific career, I saw and valued my independence as my ability to problem solve on my own. Today, I understand independence as my ability to figure out who to ask and when to ask for guidance. Adventitious Roots is yet another great resource to ask for and deliver support. You can submit to join our Slack channel here!

We are currently recruiting a new social media manager and director. Feel free to reach out to us directly at frontandcenterps [at] gmail [dot] com if you’d like to learn more about Front and Center, how you can contribute, and how we can help you connect with Black, Indigenous, and Black plant biologists.

Molecular teamwork: how three protein families and DNA work together to control gene expression

/in /by

Hong and Rusnak et al. explore how a 1000-bp region of DNA activates gene expression in giant cells.

By Adrienne Roeder and Byron Rusnak

Background: Specialized cell types carry out specific functions within plants. Some genes are expressed uniquely in one cell type and not expressed in other cells; these genes may be important for the function of that cell type. These cell type-specific expression patterns are created by transcription factors that bind to regions of the DNA called enhancers to regulate when and where a gene is expressed. Yet the regulatory logic behind how transcription factors that are more broadly expressed combine to create a cell type-specific expression pattern is not well understood. For example, giant cells are highly enlarged cells in the Arabidopsis sepal that control sepal curvature and promote defense from pathogens and insects. We previously identified a 1000-bp region of DNA that is sufficient to turn on the expression of a reporter gene specifically in giant cells.

Question: We asked how this 1000-bp DNA region activates gene expression specifically in giant cells.

Findings: Using Arabidopsis, we found that the combined activity of transcription factors from three families are important for generating the giant cell-specific pattern. TCP-type transcription factors promote expression from the enhancer in all epidermal cells. The transcription factor ATML1 modulates the expression level driven by the enhancer. As ATML1 protein is highly accumulated in giant cells, it can bind to the enhancer and drive high expression in giant cells. Dof transcription factors repress expression by binding to the enhancer, resulting in high expression in giant cells only. We created a conceptual model for how transcription factors whose encoding genes are expressed broadly in many cell types can bind to the same enhancer, combining their activities to produce cell type-specific expression patterns.

Model for how three different kinds of transcription factors combine on the enhancer to create giant cell specific expression.

Next steps: A future challenge will be to use this information as a basis for engineering new synthetic enhancers with cell type-specific expression.

Reference:

Lilan Hong, Byron Rusnak, Clint S. Ko, Shouling Xu, Xi He, Dengying Qiu, S. Earl Kang, Jose L. Pruneda-Paz, Adrienne H. K. Roeder. (2023). Enhancer activation via TCP and HD-ZIP and repression by Dof transcription factors mediate giant cell-specific expression. https://doi.org/10.1093/plcell/koad054

Strawberry inflorescence diversity: meet the thyrse

/in /by

Lembinen et al. explore the molecular mechanisms underlying inflorescence diversity in strawberry.

Sergei Lembinen1, Mikolaj Cieslak2, Teng Zhang1, Kathryn Mackenzie1, Paula Elomaa1, Przemyslaw Prusinkiewicz2, Timo Hytönen1.

1 Department of Agricultural Sciences, Viikki Plant Science Centre, University of Helsinki, P.O. Box 27, FIN-00014 Helsinki, Finland

2 Department of Computer Science, University of Calgary, Calgary, AB T2N 1N4

Background: Plants organize their flowers into clusters called inflorescences. The branching patterns and architecture of these clusters are crucial to a plant’s reproductive success and agricultural yield. The extensive variability of inflorescence architectures in strawberries was documented a century ago. Since then, inconsistent characterizations of strawberry inflorescence architectures have accumulated. To clarify these inconsistencies, we studied the architecture and development of strawberry inflorescences at the macro and micro scales using diploid woodland strawberry (Fragaria vesca) as a model plant.

Question: We wanted to understand how the diversity of strawberry inflorescences is regulated at developmental and molecular levels.

Findings: Woodland strawberries produce compound inflorescences that consist of a primary monopodial axis bearing sympodial lateral branches. The primary axis and lateral branches are produced by geometrically distinct meristems. The resulting architecture, known as a thyrse, is not found in other previously studied model plants. The diversity of thyrse architecture originates from a variable number of lateral branches on the primary axis and a variable number of sympodial branching iterations. At the molecular level, both numbers are controlled by two homologous proteins, TERMINAL FLOWER 1 (FvTFL1) and FLOWERING LOCUS T1 (FvFT1), which regulate the timing of cessation of branching. The observed diversity of woodland strawberry inflorescences has been reproduced using a computational model that takes into account the functions of FvTFL1 and FvFT1.

Next steps: Detailed molecular level mechanisms that drive the differences between the meristems and create thyrse architecture should be discovered to facilitate our understanding of the evolution of the morphological diversity in nature. This knowledge can be translated into the development of new breeding strategies to optimize the yield and quality of berries in cultivated strawberry.

Reference:

Sergei Lembinen, Mikolaj Cieslak, Teng Zhang, Kathryn Mackenzie, Paula Elomaa, Przemyslaw Prusinkiewicz, Timo Hytönen. (2023). Diversity of woodland strawberry inflorescences arises from heterochrony regulated by TERMINAL FLOWER 1 and FLOWERING LOCUS T. https://doi.org/10.1093/plcell/koad086

The dark side of the plant: lipid metabolism regulation under starvation

/in /by

Luzarowska et al. reveal that an enzyme involved in fatty acid elongation and wax synthesis determines the differential accumulation of polyunsaturated triacylglycerols.

By Corina Mariana Fusari1 & Yariv Brotman2

1Centro de Estudios Fotosintéticos y Bioquímicos (CEFOBI-CONICET-UNR), Suipacha 570, S2000LRJ Rosario, Argentina

2Department of Life Sciences, Ben Gurion University of the Negev, Beersheva, Israel

Background: In the light, plants use photosynthesis to produce sugars and grow, while in the dark, they mainly use starch as the source of energy for maintenance throughout the night. When dark conditions last for a long time, plants consume all the available starch and enter a starvation mode, where they start feeding on lipids to support their metabolism. Although metabolism affects many responses, its genetic regulation is still underexplored. The study of complex traits such as metabolism can be facilitated by combining the use of natural populations and metabolomics. This strategy, called metabolomic-GWAS (Genome Wide Association Studies) enables the identification of genes involved in variation of multiple metabolic features under diverse environmental set-ups.

Question: How is metabolism controlled upon stress? What are the genes acting behind a metabolic response to environmental fluctuations? How did plants evolve to cope with adverse environmental conditions?

Findings: We were interested in determining the genetic regulation behind the adjustment in lipid metabolism in Arabidopsis after the sudden onset of abiotic stresses (focusing on heat and dark). The interesting finding of our work is that KCS4, an enzyme involved in the elongation of fatty acids and wax synthesis, determines the differential accumulation of polyunsaturated triacylglycerols. By sequestering the saturated triacylglycerols into wax, KCS4 leaves free polyunsaturated triacylglycerols to accumulate in lipid bodies and to be used as an alternative source of energy.

Next steps: This approach could further be used to explore the fine-tuning of lipid metabolism in diverse environments and in other plant species.

Reference:

Urszula Luzarowska, Anne-Kathrin Ruß, Jérôme Joubès, Marguerite Batsale, Jędrzej Szymański, Venkatesh Periyakavanam Thirumalaikumar, Marcin Luzarowski, Si Wu, Feng Zhu, Niklas Endres, Sarah Khedhayir, Julia Schumacher, Weronika Jasinska, Ke Xu, Sandra Marcela Correa Cordoba, Simy Weil, Aleksandra Skirycz, Alisdair Robert Fernie, Yonghua Li-Beisson, Corina M. Fusari, Yariv Brotman. (2023). Hello darkness, my old friend: 3-KETOACYL-COENZYME A SYNTHASE4 is a branch point in the regulation of triacylglycerol synthesis in Arabidopsis thaliana https://doi.org/10.1093/plcell/koad059

Residues required for polar localization of rice Si transporter

/in /by

Konishi et al. explore the mechanism underlying the polar localization of a silicon transporter.

By Noriyuki Konishi, Namiki Mitani-Ueno, Naoki Yamaji and Jian Feng Ma

Institute of Plant Science and Resources, Okayama University, Chuo 2-20-1, Kurashiki, 710-0046 Japan

Background: Silicon (Si) is a beneficial element for plants. Rice (Oryza sativa) can accumulate Si in shoots up to 10% of dry weight; this accumulation helps alleviate various stresses and is essential for stable and high production of rice. The high Si accumulation in rice is achieved by the cooperation of two Si transporters, LOW SILICON 1 and 2 (OsLsi1 and OsLsi2) expressed in the roots. OsLsi1, a channel-type transporter, is present in the plasma membrane of the root exodermis and endodermis and localizes to the outer side of the cell toward the soil (distally localized). OsLsi2, an efflux type transporter, is oppositely localized at the inner side (proximally localized) of the same cells. OsLsi1 and OsLsi2 form an efficient pathway for Si uptake in rice roots.

Question: What is the mechanism underlying the polar localization of these transporters? How important is the polar localization in efficient Si uptake?

Findings: With deletion and site-directed mutation approaches, we identified the critical amino acid residues required for the polar localization of OsLsi1. They are Ile18, Ile285, and positively charged residues from the N- and C-terminal cytosolic regions of OsLsi1. Interestingly, phosphorylation, ubiquitination, and clathrin-mediated endocytosis are not involved in the polar localization. Furthermore, comparing Si uptake between plants carrying polar or non-polar OsLsi1 variants showed that polar localization of OsLsi1 plays a significant role in efficient Si uptake.

Next steps: The factors that interact with OsLsi1 for its polar localization remain to be determined. Other mechanisms involved in the polar localization of mineral element transporters also need to be investigated, especially in crops such as rice.

Reference:

Noriyuki Konishi, Namiki Mitani-Ueno, Naoki Yamaji and Jian Feng Ma. (2023). Polar localization of a rice silicon transporter requires isoleucine at both C- and N-termini as well as positively charged residues. https://doi.org/10.1093/plcell/koad073

How plants fine tune wax biosynthesis

/in /by

Huang et al. find that a 3-KETOACYL-COA SYNTHASE negatively regulates wax biosynthesis, revealing a mechanism for fine-tuning lipid metabolism.

Haodong Huang, Xianpeng Yang, Shiyou Lü and Huayan Zhao

State Key Laboratory of Biocatalysis and Enzyme Engineering, School of Life Sciences, Hubei University, Wuhan, China

College of Life Sciences, Shandong Normal University, Jinan, China

 Background: In plants, lipids play key roles as components of cellular membranes and the cuticle (the waxy covering of plant leaves and other organs), and as storage compounds in oil-seed plants. 3-KETOACYL-COA SYNTHASE (KCS) enzymes are classified into two subgroups, with one subgroup displaying fatty acid elongase (FAE) activity and the other lacking enzymatic activity.  KCSs with enzymatic activity are components of the FAE complex involved in producing very-long-chain fatty acids with chain length specificity, providing precursors for the synthesis of various lipids, including membrane lipids, surface lipids, and storage lipids. However, the precise function of the non-enzymatic group of KCSs remains to be identified.

Question: Are KCSs lacking canonical FAE activity also involved in lipid synthesis? If so, how do they function?

Findings: Here we report that Arabidopsis KCS3, which was previously shown to lack canonical catalytic activity, functions as a negative regulator of wax metabolism by reducing the enzymatic activity of KCS6, a key KCS involved in wax production. We reveal that the role of KCS3 in regulating KCS6 activity involves physical interactions between KCSs and subunits of the fatty acid elongation (FAE) complex and is essential for maintaining wax homeostasis. We also show that the regulatory role of the KCS3-KCS6 module in wax synthesis is highly conserved across diverse plant taxa from the flowering plant Arabidopsis to the moss Physcomitrium patens.

Next steps: We demonstrated that KCS3 plays a role in regulating wax synthesis, implying that other known KCSs lacking canonical FAE catalytic activity might have similar functions in lipid synthesis. To test this notion, we will examine the roles of additional KCSs lacking FAE activity, seek the possible regulatory targets of these KCSs, and study the interactions of these KCSs with their targets.

Reference:

Haodong Huang, Xianpeng Yang, Minglü Zheng, Zexi Chen, Zhuo Yang, Pan Wu, Matthew A. Jenks, Guangchao Wang, Tao Feng, Li Liu, Pingfang Yang, Shiyou Lü, Huayan Zhao (2023) An ancestral role for 3-KETOACYL-COA SYNTHASE3 as a negative regulator of plant cuticular wax synthesis. https://doi.org/10.1093/plcell/koad051

Ligands and regulatory properties of the HD-ZIPIII START domain

/in /by

Husbands et al. identify ligands and regulatory properties of the HD-ZIPIII START domain.

By By Aman Y. Husbands (University of Pennsylvania) and Marja C.P. Timmermans (University of Tuebingen).

Background: Development has been compared to a ball rolling down a hill. Cells initially have broad potential, but over time, they make decisions based on local cues which set them down a path to differentiation. Along this trajectory, thousands of genes need to be turned off or on in a carefully choreographed manner to ensure specialized identity. This is accomplished in part by transcription factors whose activities are precisely controlled by inputs operating across multiple regulatory levels. Here, we study the regulation of CLASS III HOMEODOMAIN LEUCINE ZIPPER (HD-ZIPIII) proteins, a 725-million-year-old family of transcription factors that were redeployed throughout evolution to impact nearly all aspects of plant development.

Question: HD-ZIPIII proteins contain a START domain, an evolutionarily ubiquitous module that binds lipophilic ligands. The hypothesis thus arose that HD-ZIPIII activity may be controlled by lipid ligand inputs. Remarkably, both the ligands and regulatory properties of the HD-ZIPIII START domain have remained unknown for over twenty years. The goal of our study was to resolve this long-standing mystery.

Findings: We find that the START domain promotes HD-ZIPIII dimerization and increases their transcriptional potency. We also identify several phospholipid ligands bound by the HD-ZIPIII START domain, and show that perturbing ligand binding abolishes DNA-binding competence. Thus, the START domain turns HD-ZIPIII proteins into potent DNA-binding competent transcription factors but only if they can bind and respond to their phospholipid ligands. Our findings further highlight the remarkably flexible and diverse regulatory potential of START domains.

Next steps: Having established START regulatory properties for an HD-ZIPIII protein in Arabidopsis, we are now considering our findings from an evolutionary perspective. How and when did these regulatory properties come about? Is there functional divergence of START regulation of HD-ZIPIII activity? And how are START domains able to employ such a diverse set of regulatory mechanisms?

Reference:

Aman Y. Husbands, Antje Feller, Vasudha Aggarwal, Courtney E. Dresden, Ashton S. Holub, Taekjip Ha, Marja C.P. Timmermans. (2023). The START domain potentiates HD-ZIPIII transcriptional activity. https://doi.org/10.1093/plcell/koad058

Inhibition of SIZ1-mediated HLS1 SUMOylation promotes light-induced apical hook opening

/in /by

Xiong and Yang et al. explore how plants regulate rapid opening of the apical hook in the light.

By Jiawei Xiong and Dawei Zhang, Ministry of Education Key Laboratory for Bio-Resource and Eco-Environment, College of Life Science, State Key Laboratory of Hydraulics and Mountain River Engineering, Sichuan University, Chengdu, P.R.China.

Background: When seeds are buried in the soil and germinate, the young seedlings undergo skotomorphogenesis, in which the elongating shoot forms an apical hook. The apical hook protects cotyledons and the shoot apical meristem from mechanical injuries as the shoot emerges from the soil. After reaching the soil surface, seedlings undergo photomorphogenesis, and the apical hook quickly unfolds to allow the shoot to grow upward. HOOKLESS1 (HLS1) is a central regulator of apical hook development, as a terminal signal onto which several pathways converge.

Question: How do plants regulate the rapid opening of the apical hook in response to light by modulating HLS1 function?

Findings: The SUMO E3 ligase SIZ1 interacts with HLS1 and mediates HLS1 SUMOylation. SUMOylated HLS1 is more likely to assemble into oligomers, which are the active form of HLS1. Upon exposure to light, HY5 suppresses SIZ1 transcription, thus decreasing HLS1 SUMOylation and initiating rapid apical hook opening. Our study not only describes one post-translational modification of HLS1, but also reveals a rapid mechanism regulating apical hook opening via SIZ1-mediated SUMOylation of HLS1.

Next steps: We will further study other post-translational modifications of HLS1 in response to light, as well as the effects of SUMOylation on other biochemical functions of HLS1.

Jiawei Xiong, Fabin Yang, Fan Wei, Feng Yang, Honghui Lin, Dawei Zhang. (2023). Inhibition of SIZ1-mediated SUMOylation of HOOKLESS1 promotes light-induced apical hook opening in Arabidopsis https://doi.org/10.1093/plcell/koad072