Arabidopsis thaliana NGATHA1 transcription factor induces ABA biosynthesis by activating NCED3 gene during dehydration stress

First author: Hikaru Sato; Affiliations: RIKEN Center for Sustainable Resource Science (日本理化研究所可持续资源科学中心): Tsukuba, Japan

Corresponding author: Kazoo Shinozaki

The plant hormone abscisic acid (ABA) is accumulated after drought stress and plays critical roles in the responses to drought stress in plants, such as gene regulation, stomatal closure, seed maturation, and dormancy (休眠). Although previous reports revealed detailed molecular roles of ABA in stress responses, the factors that contribute to the drought-stress responses-in particular, regulation of ABA accumulation-remain unclear. The enzyme NINE-CIS-EPOXYCAROTENOID DIOXYGENASE 3 (NCED3) is essential for ABA biosynthesis during drought stress, and the NCED3 gene is highly induced by drought stress. In the present study, we isolated NGATHAs (NGAs) as candidate transcriptional regulators of NCED3 through a screen of a plant library harboring the transcription factors fused to a chimeric (嵌合的) repressor domain, SRDX. The NGA proteins were directly bound to a cis-element NGA-binding element (NBE) in the 5′ untranslated region (5′ UTR) of the NCED3 promoter and were suggested to be transcriptional activators of NCED3. Among the single-knockout mutants of four NGA family genes, we found that the NGATHA1 (NGA1) knockout mutant was drought-stress-sensitive with a decreased expression level of NCED3 during dehydration stress (脱水胁迫). These results suggested that NGA1 essentially functions as a transcriptional activator of NCED3 among the NGA family proteins. Moreover, the NGA1 protein was degraded under nonstressed conditions, and dehydration stress enhanced the accumulation of NGA1 proteins, even in ABA-deficient mutant plants, indicating that there should be ABA-independent posttranslational regulations (翻译后调控). These findings emphasize the regulatory mechanisms of ABA biosynthesis during early drought stress.

植物激素脱落酸ABA在干旱胁迫后积累，在植物对干旱胁迫的响应过程中扮演重要作用，比如基因调控、气孔关闭、种子成熟以及休眠。尽管之前的研究揭示了胁迫响应中ABA的分子作用，但ABA在胁迫响应下积累的调控因子仍然还不清楚。9-顺式-环氧类胡萝卜素双加氧酶NCED3作用于ABA在干旱胁迫中的生物合成，并且NCED3基因受到干旱胁迫的诱导表达。本文中，作者对基于转录因子融合进嵌合抑制结构域SRDX所构建的植物库进行了筛选，鉴定到了NCED3基因的转录调控候选因子NGAs。NGA蛋白直接结合到NCED3基因5′ UTR区域的一个顺式元件NGA结合元件，因此被认为对于NCED3基因有转录激活的作用。NGA基因家族的单突变体构建研究发现NGA1基因敲除突变体植株对于干旱敏感，并且在脱水胁迫时NCED3基因的表达水平下调。这些结果说明NGA1是NGA家族中能够转录激活NCED3基因的蛋白。此外，NGA1在非胁迫的条件下会降解，并且脱水胁迫会增加NGA1蛋白的积累，甚至在ABA缺陷型突变体中也同样如此，说明并定存在一个不依赖于ABA的翻译后调控机制发挥作用。本文的研究揭示了植物干旱胁迫时ABA生物合成的分子调控机制。

通讯：Kazuo Shinozaki  (http://www.csrs.riken.jp/en/labs/gdrg/)

个人简介：1977年，日本名古屋大学，博士；1987年，美国洛克菲勒大学，访问学者。

研究方向：植物性状改良相关基因的鉴定；最小化环境胁迫、最大化植株产量相关基因的鉴定。

doi: https://doi.org/10.1073/pnas.1811491115

Journal: PNAS

First Published: 05 November, 2018

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