谢旗研究组PLoS解析种子休眠调控机制

中国科学院遗传与发育生物学研究所谢旗实验室深入研究了ABI4在调控种子休眠中的分子功能，证实ABI4通过正调控种子中ABA的合成、负调控GA的合成，进而诱导种子的休眠。

　　

种子休眠是农业生产上一个重大农艺性状，适度的休眠水平对作物种子的正常收获、贮存及随后的萌发都起着关键的作用，也极大地影响着农作物的产量和品质，具有重要的经济学意义。大量研究表明，ABA与GA两种激素相互拮抗地调控种子休眠，它们在种子从休眠向萌发转换的生理过程中起到了重要的调控作用。因此，ABA与GA合成或信号传导途径的很多突变体都表现出种子休眠程度改变的表型。

ABI4是ABA信号途径中非常关键的一个正调控因子，但是到目前研究的结论是ABI4并未参与种子休眠调控。

中国科学院遗传与发育生物学研究所谢旗实验室早前鉴定了一个泛素连接酶SDIR1，发现其通过调控bZIP和ABI4这两类转录因子的基因表达，进而增强ABA信号，并参与调控种子萌发等生理学过程（Zhang et al., 2007, Plant Cell）。

随后，谢旗实验室深入研究了ABI4在调控种子休眠中的分子功能。结合遗传学、分子生物学、生物化学和植物生理学等研究方法，证实ABI4通过正调控种子中ABA的合成、负调控GA的合成，进而诱导种子的休眠。该研究澄清了学术界长期以来“ABI4没有调控种子休眠的分子功能”的认识，并指出了造成这种错误认识的原因所在。另外,过表达ABI4种子休眠程度有所降低，该研究对于防控作物种子的穗发芽具有潜在的理论指导意义。

研究结果于6月20日在线发表于PLoS Genetics杂志。谢旗实验室的博士研究生舒凯为该论文的第一作者。该工作的CHIP-PCR工作得到曹晓风研究组的大力支持。研究得到了国家自然科学基金委激素重大项目和国家蛋白研究计划项目的资助。

原文标题：

ABI4 Regulates Primary Seed Dormancy by Regulating the Biogenesis of Abscisic Acid and Gibberellins in Arabidopsis

Seed dormancy is an important economic trait for agricultural production. Abscisic acid (ABA) and Gibberellins (GA) are the primary factors that regulate the transition from dormancy to germination, and they regulate this process antagonistically. The detailed regulatory mechanism involving crosstalk between ABA and GA, which underlies seed dormancy, requires further elucidation. Here, we report that ABI4 positively regulates primary seed dormancy, while negatively regulating cotyledon greening, by mediating the biogenesis of ABA and GA. Seeds of the Arabidopsis abi4 mutant that were subjected to short-term storage (one or two weeks) germinated significantly more quickly than Wild-Type (WT), and abi4 cotyledons greened markedly more quickly than WT, while the rates of germination and greening were comparable when the seeds were subjected to longer-term storage (six months). The ABA content of dry abi4 seeds was remarkably lower than that of WT, but the amounts were comparable after stratification. Consistently, the GA level of abi4 seeds was increased compared to WT. Further analysis showed that abi4 was resistant to treatment with paclobutrazol (PAC), a GA biosynthesis inhibitor, during germination, while OE-ABI4 was sensitive to PAC, and exogenous GA rescued the delayed germination phenotype of OE-ABI4. Analysis by qRT-PCR showed that the expression of genes involved in ABA and GA metabolism in dry and germinating seeds corresponded to hormonal measurements. Moreover, chromatin immunoprecipitation qPCR (ChIP-qPCR) and transient expression analysis showed that ABI4 repressed CYP707A1 and CYP707A2 expression by directly binding to those promoters, and the ABI4 binding elements are essential for this repression. Accordingly, further genetic analysis showed that abi4 recovered the delayed germination phenotype of cyp707a1 and cyp707a2 and further, rescued the non-germinating phenotype of ga1-t. Taken together, this study suggests that ABI4 is a key factor that regulates primary seed dormancy by mediating the balance between ABA and GA biogenesis.