Plant Cell:西北农林管清美团队揭示转座子MITE-MdRF1通过影响表达进而调控苹果抗旱的分MdRFNR1-1子机制

今天介绍的是由西北农林科技大学管清美团队在The Plant Cell上发表的研究论文《Methylation of a MITE insertion in the MdRFNR1-1 promoter is positively associated with its allelic expression in apple in response to drought stress》。

干旱胁迫严重影响苹果的生长和果实产量，氧化还原调节途径对于植物对干旱的反应很重要。据作者团队先前表明，根型铁氧还蛋白NADP+氧化还原酶1基因（RFNR1）的表达是由苹果中的聚乙二醇诱导的，但MdRFNR1是否参与该作物的耐旱性以及干旱诱导后的分子机制尚不清楚。转座因子（TE）是DNA片段的移动单元，可以在基因组中自动复制，并在基因调控和染色体结构中发挥重要作用。大多数TE在维持基因组稳定性方面是不活跃的，但是其中有些在植物进化和环境适应中起着重要作用。它通过产生遗传和表观遗传的变异而产生新的基因表达模式，进而影响植物的生长发育和抗逆性状，例如血橙的红色和玉米的抗旱。但是转座子在植物抗逆胁迫响应中的作用尚未明。

为了研究MdRFNR1的功能，作者从GL-3（皇家嘎啦的后代，用作苹果转基因背景材料）中克隆MDRFNR1。有两个具有三个氨基酸差异的等位基因编码MDRFNR1，作者将它们命名为MdRFNR1-1和MDRFNR 1-2。进一步测序和比对后，作者在MDRFNR 1-1的启动子中发现了430bp的MITE插入，并将其命名为MITE-MdRF1。通过PEG模拟干旱处理、GUS实验和PCR基因分型，作者证明了MdRFNR1通过调节氧化还原系统，包括增加NADP+积累、过氧化氢酶和过氧化物酶活性以及降低NADP水平，在耐旱性中发挥积极作用；序列分析鉴定了MITE-MdRF1不是MDRFNR-2平行序列；干旱胁迫显著诱导了MdRFNR1-1而非MDRFNR2的表达，这与MITE插入及其DNA甲基化呈正相关。也揭示了MITE-MdRF1在诱导MdRFNR1-1表达以及苹果干旱反应中的分子作用，以及多年生树木自然变异的分子机制。简而言之，苹果铁氧还蛋白NADP+氧化还原酶基因的等位基因表达是通过一种识别其启动子中MITE的插入的甲基化的复合物来促进的，从而应对干旱胁迫。

Drought stress seriously affects the growth and fruit yield of apples. The redox regulatory pathway is important forplant 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.Transposable elements (TEs) are mobile units of DNA fragments that can replicate 2autonomously in the genome and play important roles  in gene regulation and chromosome architecture. Most TEs are inactive to maintain genome stability , whereas some play important roles in plant evolution and environmental adaption.It creates genetic and epigenetic variations to create new gene expression patterns that affect growth, development and resilience traits, such as the redness of blood oranges and drought resistance in maize. However, the role of transposons in plant response to stress has not been clarified. To  investigate the function of MdRFNR1, we cloned MdRFNR1from GL-3(the progeny of Royal   Gala apple,which was used as the background for apple transformation). There were two alleles encoding MdRFNR1 with three amino acid differences. We named these proteins MdRFNR1-1 and MdRFNR1-2. After sequencing and alignment, we identified a 430 bp MITE insertion in the promoter of MdRFNR1-1, and we named this insertion MITE-MdRF1. MdRFNR1 plays a positive role in drought tolerance by regulating the redox system, including increasing NADP+ accumulation and catalase and peroxidase activities and decreasing NADPH levels.

Sequence analysis identified a MITE insertion (MITE-MdRF1) in the promoter of MdRFNR1-1 but not the MdRFNR1-2 allele. MdRFNR1-1 but not MdRFNR1-2 expression was significantly induced by drought stress, which was positively associated with the MITE-MdRF1 insertion and its DNA methylation.These findings illustrate the molecular roles of methylated MITE-MdRF1 in induced MdRFNR1-1 expression as well as the drought response of apple and shed light on the molecular mechanisms of natural variation in perennial trees.Allelic expression of a ferredoxin-NADP+oxidoreductasegenein apple is  promoted by acomplexthatrecognizesmethylation in a MITE insertion in its promoter in response to drought stress.

原文链接：https://doi.org/10.1093/plcell/koac220

转自：“植物科学SCI”微信公众号

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