Department of Biological Sciences, Faculty of Science, National University of Singapore, Singapore 117543, Singapore.
BMC Plant Biol. 2012 Oct 4;12:179. doi: 10.1186/1471-2229-12-179.
Seed germination is of immense significance for agriculture and has been studied for centuries. Yet, our understanding of the molecular mechanisms underlying regulation of dormancy and germination is still in its infancy. Gibberellins are the key phytohormones that promote germination, and the DELLA protein RGL2 is the main signalling intermediate involved in this response. Germination is completely inhibited if functional RGL2 is overexpressed and/or stabilized; however, the molecular mechanisms of RGL2 function are still largely unknown. We therefore attempted to shed light onto some of the genetic events downstream of RGL2.
Gene ontology of the transcriptome differentially regulated by RGL2, as well as extensive cross-comparison with other available microarray data indicates that RGL2-mediated inhibition of germination causes seeds to enter a state of dormancy. RGL2 also appears to differentially regulate a number of transcription factors, many of which are known to be involved in light- or phytohormone-mediated aspects of germination. A promoter analysis of differentially expressed genes identified an enrichment of several motifs that can be bound by specific transcription factors, for example GAMYB, ARF1, or Dof-type zinc fingers. We show that Dof-binding motifs indeed play a role in RGL2-mediated transcription. Using Chromatin Immunoprecipitation (ChIP), we show that RGL2 directly downregulates at least one cell wall modifying enzyme, which is predicted to constrain cell growth thereby leading to inhibition of seed germination.
Our results reveal that RGL2 controls various aspects of germination. Through the repression of cell wall modifying enzymes, cell growth is directly constrained to inhibit germination. Furthermore, RGL2 likely interacts with various types of proteins to regulate transcription, and differentially regulates several transcription factors. Collectively, our data indicate that gibberellins, acting via RGL2, control several aspects of seed germination.
种子萌发对于农业具有重要意义，已经研究了几个世纪。然而，我们对休眠和萌发调控的分子机制的理解仍处于起步阶段。赤霉素是促进萌发的关键植物激素，DELLA 蛋白 RGL2 是参与这一反应的主要信号中间物。如果功能性 RGL2 过表达和/或稳定化，萌发将完全受到抑制；然而，RGL2 功能的分子机制在很大程度上仍然未知。因此，我们试图阐明 RGL2 下游的一些遗传事件。
RGL2 差异调控的转录组的基因本体论，以及与其他可用微阵列数据的广泛交叉比较表明，RGL2 介导的萌发抑制导致种子进入休眠状态。RGL2 似乎也差异调控许多转录因子，其中许多已知参与光或植物激素介导的萌发。差异表达基因的启动子分析鉴定了几个可以被特定转录因子结合的基序的富集，例如 GAMYB、ARF1 或 Dof 型锌指。我们表明，Dof 结合基序确实在 RGL2 介导的转录中起作用。使用染色质免疫沉淀（ChIP），我们表明 RGL2 直接下调至少一种细胞壁修饰酶，该酶预计会限制细胞生长，从而导致种子萌发的抑制。
我们的结果揭示了 RGL2 控制萌发的各个方面。通过抑制细胞壁修饰酶，直接限制细胞生长以抑制萌发。此外，RGL2 可能与各种类型的蛋白质相互作用以调节转录，并差异调控几种转录因子。总之，我们的数据表明，赤霉素通过 RGL2 控制种子萌发的几个方面。
