A fresh mechanism for drought tolerance in apple

Niu, Jiang, Cao et al. discover the role of a ferredoxin-NADP+ oxidoreductase gene in drought tolerance in apple.

Background: Global climate change and rapid population growth have been increasing the shortage of water resources, enhancing the effects of natural disasters such as drought. Drought stress seriously affects the growth and fruit yield of apples. The redox regulatory pathway is important for plant responses to drought. We previously showed that the expression of the root-type ferredoxin-NADP+ oxidoreductase 1 gene (RFNR1) is induced by polyethylene glycol in apple, but whether MdRFNR1 is involved in the drought tolerance of this crop and the molecular mechanism behind its induction by drought are unclear.

Question: How does drought stress affect the expression of MdRFNR1 in apple? Does MdRFNR1 affect the drought tolerance of apple?

 Findings: We found that MdRFNR1 increases the drought tolerance of apple by regulating the redox system, including facilitating NADP+ accumulation and CAT and POD activities and decreasing NADPH levels. Sequence analysis revealed that a MITE transposon element, MITE-MdRF1, is inserted in the promoter of an MdRFNR1 allele (MdRFNR1-1). MITE-MdRF1 plays an essential role in simulated drought-induced MdRFNR1-1 expression, and this induction is associated with methylated MITE-MdRF1. Further study revealed that a protein complex comprising the transcriptional anti-silencing factor MdSUVH and the DNAJ domain-containing protein DNAJ promotes the expression of the MdRFNR1-1 allele in response to drought via methylated MITE-MdRF1. Thus, our data reveal the molecular mechanism of the MdSUVH-MdDNAJ–MITE-MdRF1–MdRFNR1-1 regulatory module in promoting drought tolerance in apple.

Next steps: Our study revealed a mechanism by which methylated MITE-MdRF1 promotes the expression of MdRFNR1-1. Whether other factors are involved in this process is unclear. For instance, which transcription factors recognize the cis-element in MITE-MdRF1? We will continue to explore the potential mechanism behind this process in the future.

Chundong Niu, Lijuan Jiang, Fuguo Cao, Chen Liu, Junxing Guo, Zitong Zhang, Qianyu Yue, Nan Hou, Zeyuan Liu, Xuewei Li, Muhammad Mobeen Tahir, Jieqiang He, Zhongxing Li, Chao Li, Fengwang Ma, Qingmei Guan (2022). Methylation of a MITE insertion in the MdRFNR1-1 promoter is positively associated with its allelic expression in apple in response to drought stress. https://doi.org/10.1093/plcell/koac220