Kim Suk-Hwan, Yoon Jungwon, Kim Hanna, Lee Sang-Ji, Paek Nam-Chon
Department of Agriculture, Forestry and Bioresources, Plant Genomics and Breeding Institute, Research Institute of Agriculture and Life Sciences, Seoul National University, Seoul, Republic of Korea.
Rice (N Y). 2023 Dec 13;16(1):60. doi: 10.1186/s12284-023-00673-w.
Leaf senescence represents the final phase of leaf development and is characterized by a highly organized degenerative process involving the active translocation of nutrients from senescing leaves to growing tissues or storage organs. To date, a large number of senescence-associated transcription factors (sen-TFs) have been identified that regulate the initiation and progression of leaf senescence. Many of these TFs, including NAC (NAM/ATAF1/2/CUC2), WRKY, and MYB TFs, have been implicated in modulating the expression of downstream senescence-associated genes (SAGs) and chlorophyll degradation genes (CDGs) under the control of phytohormones. However, the involvement of basic helix-loop-helix (bHLH) TFs in leaf senescence has been less investigated. Here, we show that OsbHLH079 delays both natural senescence and dark-induced senescence: Overexpression of OsbHLH079 led to a stay-green phenotype, whereas osbhlh079 knockout mutation displayed accelerated leaf senescence. Similar to other sen-TFs, OsbHLH079 showed a gradual escalation in expression as leaves underwent senescence. During this process, the mRNA levels of SAGs and CDGs remained relatively low in OsbHLH079 overexpressors, but increased sharply in osbhlh079 mutants, suggesting that OsbHLH079 negatively regulates the transcription of SAGs and CDGs under senescence conditions. Additionally, we found that OsbHLH079 delays ABA-induced senescence. Subsequent RT-qPCR and dual-luciferase reporter assays revealed that OsbHLH079 downregulates the expression of ABA signaling genes, such as OsABF2, OsABF4, OsABI5, and OsNAP. Taken together, these results demonstrate that OsbHLH079 functions in delaying leaf yellowing by attenuating the ABA responses.
叶片衰老代表叶片发育的最后阶段，其特征是一个高度有序的退化过程，涉及营养物质从衰老叶片向生长组织或储存器官的主动转运。到目前为止，已经鉴定出大量衰老相关转录因子（sen-TFs），它们调节叶片衰老的起始和进程。这些转录因子中的许多，包括NAC（NAM/ATAF1/2/CUC2）、WRKY和MYB转录因子，已被证明在植物激素的控制下调节下游衰老相关基因（SAGs）和叶绿素降解基因（CDGs）的表达。然而，基本螺旋-环-螺旋（bHLH）转录因子在叶片衰老中的作用研究较少。在这里，我们表明OsbHLH079延迟自然衰老和黑暗诱导的衰老：OsbHLH079的过表达导致持绿表型，而osbhlh079敲除突变体表现出加速的叶片衰老。与其他sen-TFs类似，随着叶片衰老，OsbHLH079的表达逐渐升高。在此过程中，SAGs和CDGs的mRNA水平在OsbHLH079过表达植株中相对较低，但在osbhlh079突变体中急剧增加，这表明OsbHLH079在衰老条件下负调控SAGs和CDGs的转录。此外，我们发现OsbHLH079延迟ABA诱导的衰老。随后的RT-qPCR和双荧光素酶报告基因分析表明，OsbHLH079下调ABA信号基因如OsABF2、OsABF4、OsABI5和OsNAP的表达。综上所述，这些结果表明OsbHLH079通过减弱ABA反应在延迟叶片变黄中发挥作用。
