State Key Laboratory of Crop Stress Biology for Arid Areas, College of Life Sciences, Northwest A & F University, Yangling, Shaanxi, 712100, China.
Department of Biology, University of British Columbia, Okanagan Campus, Kelowna, BC, V1V 1V7, Canada.
Plant J. 2020 Sep;104(1):171-184. doi: 10.1111/tpj.14914. Epub 2020 Jul 29.
Leaf senescence represents the final stage of leaf growth and development, and its onset and progression are strictly regulated; however, the underlying regulatory mechanisms remain largely unknown. In this study we found that WRKY42 was highly induced during leaf senescence. Loss-of-function wrky42 mutants showed delayed leaf senescence whereas the overexpression of WRKY42 accelerated senescence. Transcriptome analysis revealed 2721 differentially expressed genes between wild-type and WRKY42-overexpressing plants, including genes involved in salicylic acid (SA) and reactive oxygen species (ROS) synthesis as well as several senescence-associated genes (SAGs). Moreover, WRKY42 activated the transcription of isochorismate synthase 1 (ICS1), respiratory burst oxidase homolog F (RbohF) and a few SAG genes. Consistently, the expression of these genes was reduced in wrky42 mutants but was markedly increased in transgenic Arabidopsis overexpressing WRKY42. Both in vitro electrophoretic mobility shift assays (EMSAs) and in vivo chromatin immunoprecipitation and dual luciferase assays demonstrated that WRKY42 directly bound to the promoters of ICS1 and RbohF, as well as a few SAGs, to activate their expression. Genetic analysis further showed that mutations of ICS1 and RbohF suppressed the early senescence phenotype evoked by WRKY42 overexpression. Thus, we have identified WRKY42 as a novel transcription factor positively regulating leaf senescence by directly activating the transcription of ICS1, RbohF and SAGs, without any seed yield penalty.
叶片衰老代表了叶片生长和发育的最后阶段，其起始和进程受到严格调控；然而，其背后的调控机制在很大程度上仍然未知。在本研究中，我们发现 WRKY42 在叶片衰老过程中高度诱导。wrky42 功能丧失突变体表现出叶片衰老延迟，而过表达 WRKY42 则加速衰老。转录组分析显示，野生型和 WRKY42 过表达植株之间有 2721 个差异表达基因，包括参与水杨酸（SA）和活性氧（ROS）合成以及几个衰老相关基因（SAGs）的基因。此外，WRKY42 激活异分支酸合酶 1（ICS1）、呼吸爆发氧化酶同源物 F（RbohF）和几个 SAG 基因的转录。一致地，这些基因在 wrky42 突变体中的表达减少，但在过表达 WRKY42 的转基因拟南芥中显著增加。体外电泳迁移率变动分析（EMSA）和体内染色质免疫沉淀和双荧光素酶测定表明，WRKY42 直接结合到 ICS1 和 RbohF 以及几个 SAG 基因的启动子上，激活它们的表达。遗传分析进一步表明，ICS1 和 RbohF 的突变抑制了 WRKY42 过表达引起的早期衰老表型。因此，我们已经确定 WRKY42 是一种新型转录因子，通过直接激活 ICS1、RbohF 和 SAGs 的转录来正向调控叶片衰老，而不会对种子产量造成任何影响。
