Multilayered regulation of membrane-bound ONAC054 is essential for abscisic acid-induced leaf senescence in rice

First author: Yasuhito Sakuraba; Affiliations: The University of Tokyo (东京大学): Tokyo, Japan

Corresponding author: Nam-Chon Paek

In most plants, abscisic acid (ABA) induces premature leaf senescence; however, the mechanisms of ABA signaling during leaf senescence remain largely unknown. Here, we show that the rice (Oryza sativa) NAM/ATAF½/CUC2 (NAC) transcription factor ONAC054 plays an important role in ABA-induced leaf senescence. onac054 knockout mutants maintained green leaves, while ONAC054-overexpressing lines showed early leaf yellowing under dark- and ABA-induced senescence conditions. Genome-wide microarray analysis showed that ABA signaling-associated genes, including ABA INSENSITIVE5 (OsABI5) and senescence-associated genes, including STAY-GREEN and NON-YELLOW COLORING1 (NYC1), were significantly downregulated in onac054 mutants. Chromatin immunoprecipitation and protoplast transient assays showed that ONAC054 directly activates OsABI5 and NYC1 by binding to the mitochondrial dysfunction motif in their promoters. ONAC054 activity is regulated by proteolytic processing of the C-terminal transmembrane domain (TMD). We found that nuclear import of ONAC054 requires cleavage of the putative C-terminal TMD. Furthermore, the ONAC054 transcript (termed ONAC054α) has an alternatively spliced form (ONAC054β), with seven nucleotides inserted between intron 5 and exon 6, truncating ONAC054α protein at a premature stop codon. ONAC054β lacks the TMD and thus localizes to the nucleus. The significance of this multilayered regulation of ONAC054 for ABA-induced leaf senescence is also discussed.

在大多数的植物中，脱落酸ABA会诱导叶片的提前衰老，然而叶片衰老过程中ABA信号通路的分子机制还存在很多未知。本文中，作者发现水稻NAC转录因子ONAC054在ABA诱导的叶片衰老过程中发挥重要作用。在黑暗和ABA诱导的条件下，onac054敲除突变体保持了绿色的叶片，而ONAC054过表达突变体叶片很早就开始变黄。全基因组的芯片分析显示包括OsABI5在内的ABA信号通路相关基因和包括STAY-GREEN和NYC1在内的衰老相关基因在onac054突变体中表达量显著下调。染色质免疫功沉淀和原生质体瞬间表达分析均表明ONAC054能够通过结合到OsABI5和NYC1基因启动子中的线粒体功能紊乱基序，直接激活他们的表达。ONAC054蛋白C端跨膜结构域的蛋白水解能够调控其本身的活性。作者发现ONAC054蛋白进入细胞核需要先将C端跨膜结构域剪切掉。此外，ONAC054的转录本ONAC054α具有一个可变剪切体ONAC054β，7个核苷酸插入到第5个内含子和第6个外显子之间，导致了ONAC054α被提前终止。ONAC054β缺少跨膜结构域，因此定位于细胞核中。作者还讨论了ONAC054对于ABA诱导的叶片衰老多个层次的调控作用。

通讯：Nam-Chon Paek (http://cals.snu.ac.kr/en/about/organization/search/faculty?mode=view&profidx=50)

个人简介：1981-1985年，首尔国立大学，学士；1985-1987年，首尔国立大学，硕士；1990-1994年，德克萨斯A&M大学，博士。

研究方向：作物分子遗传。

doi: https://doi.org/10.1105/tpc.19.00569

Journal: Plant Cell

First Published: January 06, 2020