Cao Dongni, Hussain Alamgir, Cheng Hui, Peng Jinrong
Institute of Molecular and Cell Biology, 61 Biopolis Drive, Proteos 138673, Singapore.
Planta. 2005 Dec;223(1):105-13. doi: 10.1007/s00425-005-0057-3. Epub 2005 Jul 21.
The Arabidopsis severe gibberellin-deficient mutant ga1-3 does not germinate even when the optimal light and temperature conditions are provided. This fact suggests that (1) gibberellin (GA) is absolutely necessary for the germination of an intact seed and (2) the ga1-3 mutant can be used as a good system to identify factors that repress seed germination. In this report, using ga1-3 mutation as the genetic background, we confirm that RGL2, one member of the DELLA family, encodes the predominant repressor of seed germination in Arabidopsis and show that the other DELLA genes GAI,RGA and RGL1 enhance the function of RGL2. More importantly, we show that ga1-3 seeds lacking RGA, RGL1 and RGL2 or GAI, RGL1 and RGL2, confer GA-independent germination in the light but not in the darkness whilst ga1-3 seeds lacking GAI, RGA and RGL2 germinate both in the light and darkness. This suggests that the destabilization or inactivation of RGA and GAI is not only triggered by GA but also possibly by light. In addition, ga1-3 seeds lacking in all the aforementioned four DELLA genes have elongated epidermal cells and confer light-, cold- and GA-independent seed germination. Therefore, DELLA proteins likely act as integrators of environmental and endogenous cues to regulate seed germination.
拟南芥严重赤霉素缺陷型突变体ga1-3即使在提供最佳光照和温度条件下也不会萌发。这一事实表明：（1）赤霉素（GA）对于完整种子的萌发是绝对必需的；（2）ga1-3突变体可作为鉴定抑制种子萌发因子的良好体系。在本报告中，以ga1-3突变作为遗传背景，我们证实DELLA家族成员之一的RGL2编码拟南芥种子萌发的主要抑制因子，并表明其他DELLA基因GAI、RGA和RGL1增强了RGL2的功能。更重要的是，我们发现缺失RGA、RGL1和RGL2或GAI、RGL1和RGL2的ga1-3种子在光照下可实现不依赖GA的萌发，但在黑暗中则不能，而缺失GAI、RGA和RGL2的ga1-3种子在光照和黑暗中均可萌发。这表明RGA和GAI的去稳定化或失活不仅由GA触发，还可能由光触发。此外，缺失上述所有四个DELLA基因的ga1-3种子具有伸长的表皮细胞，并能实现不依赖光、冷和GA的种子萌发。因此，DELLA蛋白可能作为环境和内源信号的整合因子来调节种子萌发。
