Kim Yun Young, Cui Mei Hua, Noh Min Soo, Jung Kwang Wook, Shin Jeong Sheop
Division of Life Sciences, Korea University, Seoul 136-701, Korea.
School of Life Sciences and Biotechnology, Shanghai JiaoTong University, Shanghai 200240, China.
Plant Cell Physiol. 2017 Mar 1;58(3):574-586. doi: 10.1093/pcp/pcx003.
ABA plays a critical role in regulating seed germination and stomatal movement in response to drought stress. Screening ABA-responsive genes led to the identification of a novel Arabidopsis gene encoding a protein which contained a conserved F-box-associated (FBA) domain, subsequently named ABA-responsive FBA domain-containing protein 1 (AFBA1). Expression of ProAFBA1:GUS revealed that this gene was mainly expressed in guard cells. Expression of AFBA1 increased following the application of exogenous ABA and exposure to salt (NaCl) and drought stresses. Seed germination of the loss-of-function mutant (afba1) was insensitive to ABA, salt or mannitol, whereas AFBA1-overexpressing (Ox) seeds were more sensitive to these stresses than the wild-type seeds. The afba1 plants showed decreased drought tolerance, increased water loss rate and ABA-insensitive stomatal movement compared with the wild-type. In contrast, AFBA1-Ox plants exhibited enhanced drought tolerance and a rapid ABA-induced stomatal closure response. The expression of genes encoding serine/threonine protein phosphatases that are known negative regulators of ABA signaling increased in afba1 plants but decreased in AFBA1-Ox plants. AFBA1 was also found to be localized in the nucleus and to interact with an R2R3-type transcription factor, MYB44, leading to the suggestion that it functions in the stabilization of MYB44. Based on these results, we suggest that AFBA1 functions as a novel positive regulator of ABA responses, regulating the expression of genes involved in ABA signal transduction in Arabidopsis through its interaction with positive regulators of ABA signaling including MYB44, and increasing their stability during ABA-mediated responses.
脱落酸（ABA）在响应干旱胁迫调节种子萌发和气孔运动中起着关键作用。对ABA响应基因的筛选导致鉴定出一个新的拟南芥基因，该基因编码一种含有保守F-box相关（FBA）结构域的蛋白质，随后将其命名为含ABA响应FBA结构域蛋白1（AFBA1）。ProAFBA1:GUS的表达表明该基因主要在保卫细胞中表达。施加外源ABA以及暴露于盐（NaCl）和干旱胁迫后，AFBA1的表达增加。功能缺失突变体（afba1）的种子萌发对ABA、盐或甘露醇不敏感，而AFBA1过表达（Ox）的种子比野生型种子对这些胁迫更敏感。与野生型相比，afba1植株表现出耐旱性降低、失水率增加和对ABA不敏感的气孔运动。相反，AFBA1-Ox植株表现出增强的耐旱性和快速的ABA诱导的气孔关闭反应。编码丝氨酸/苏氨酸蛋白磷酸酶（已知为ABA信号的负调节因子）的基因表达在afba1植株中增加，但在AFBA1-Ox植株中减少。还发现AFBA1定位于细胞核，并与R2R3型转录因子MYB44相互作用，这表明它在MYB44的稳定中起作用。基于这些结果，我们认为AFBA1作为ABA反应的一种新型正调节因子，通过与包括MYB44在内的ABA信号正调节因子相互作用，调节拟南芥中参与ABA信号转导的基因表达，并在ABA介导的反应过程中增加它们的稳定性。
