Zhou Shun-Fan, Sun Le, Valdés Ana Elisa, Engström Peter, Song Ze-Ting, Lu Sun-Jie, Liu Jian-Xiang
State Key Laboratory of Genetic Engineering, Collaborative Innovation Center of Genetics and Development, Institute of Plant Biology, School of Life Sciences, Fudan University, Shanghai, 200433, China.
Physiological Botany, Uppsala BioCenter, Uppsala University, Almas Allé 5, 75651, Uppsala, Sweden.
New Phytol. 2015 Oct;208(1):188-97. doi: 10.1111/nph.13436. Epub 2015 Apr 28.
Abscisic acid plays important roles in maintaining seed dormancy while gibberellins (GA) and other phytohormones antagonize ABA to promote germination. However, how ABA signaling is desensitized during the transition from dormancy to germination is still poorly understood. We functionally characterized the role of membrane-associated transcription factor peptidase, site-2 protease (S2P), in ABA signaling during seed germination in Arabidopsis. Genetic analysis showed that loss-of-function of S2P conferred high ABA sensitivity during seed germination, and expression of the activated form of membrane-associated transcription factor bZIP17, in which the transmembrane domain and endoplasmic reticulum (ER) lumen-facing C-terminus were deleted, in the S2P mutant rescued its ABA-sensitive phenotype. MYC and green fluorescent protein (GFP)-tagged bZIP17 were processed and translocated from the ER to the nucleus in response to ABA treatment. Furthermore, genes encoding negative regulators of ABA signaling, such as the transcription factor ATHB7 and its target genes HAB1, HAB2, HAI1 and AHG3, were up-regulated in seeds of the wild-type upon ABA treatment; this up-regulation was impaired in seeds of S2P mutants. Our results suggest that S2P desensitizes ABA signaling during seed germination through regulating the activation of the membrane-associated transcription factor bZIP17 and therefore controlling the expression level of genes encoding negative regulators of ABA signaling.
脱落酸在维持种子休眠方面发挥着重要作用，而赤霉素（GA）和其他植物激素则拮抗脱落酸以促进种子萌发。然而，在从休眠到萌发的转变过程中，脱落酸信号是如何脱敏的，目前仍知之甚少。我们对膜相关转录因子肽酶——位点2蛋白酶（S2P）在拟南芥种子萌发过程中脱落酸信号传导中的作用进行了功能表征。遗传分析表明，S2P功能缺失导致种子萌发过程中对脱落酸高度敏感，而在S2P突变体中表达缺失跨膜结构域和面向内质网（ER）腔的C末端的膜相关转录因子bZIP17的激活形式，可挽救其对脱落酸敏感的表型。响应脱落酸处理，带有MYC和绿色荧光蛋白（GFP）标签的bZIP17被加工并从内质网转运至细胞核。此外，编码脱落酸信号负调控因子的基因，如转录因子ATHB7及其靶基因HAB1、HAB2、HAI1和AHG3，在野生型种子经脱落酸处理后会上调；而在S2P突变体种子中，这种上调受到损害。我们的结果表明，S2P在种子萌发过程中通过调节膜相关转录因子bZIP17的激活来使脱落酸信号脱敏，从而控制编码脱落酸信号负调控因子的基因的表达水平。
