Kim Dong Hwan, Yamaguchi Shinjiro, Lim Soohwan, Oh Eunkyoo, Park Jeongmu, Hanada Atsushi, Kamiya Yuji, Choi Giltsu
Department of Biological Sciences, KAIST, Daejeon 305-701, Korea.
Plant Cell. 2008 May;20(5):1260-77. doi: 10.1105/tpc.108.058859. Epub 2008 May 16.
Light absorbed by seed phytochromes of Arabidopsis thaliana modulates abscisic acid (ABA) and gibberellic acid (GA) signaling pathways at least partly via PHYTOCHROME-INTERACTING FACTOR3-LIKE5 (PIL5), a phytochrome-interacting basic helix-loop-helix transcription factor. Here, we report a new mutant, somnus (som), that germinates in darkness, independently of various light regimens. SOM encodes a nucleus-localized CCCH-type zinc finger protein. The som mutant has lower levels of ABA and elevated levels of GA due to expressional changes in ABA and GA metabolic genes. Unlike PIL5, however, SOM does not regulate the expression of GA-INSENSITIVE and REPRESSOR OF GA1 (RGA/RGA1), two DELLA genes encoding GA negative signaling components. Our in vivo analysis shows that PIL5 activates the expression of SOM by binding directly to its promoter, suggesting that PIL5 regulates ABA and GA metabolic genes partly through SOM. In agreement with these results, we also observed that the reduced germination frequency of a PIL5 overexpression line is rescued by the som mutation and that this rescue is accompanied by expressional changes in ABA and GA metabolic genes. Taken together, our results indicate that SOM is a component in the phytochrome signal transduction pathway that regulates hormone metabolic genes downstream of PIL5 during seed germination.
拟南芥种子中的光敏色素吸收的光至少部分地通过与光敏色素相互作用的基本螺旋-环-螺旋转录因子类光敏色素相互作用因子3-样5（PIL5）来调节脱落酸（ABA）和赤霉素（GA）信号通路。在此，我们报道了一个新的突变体，嗜睡（som），它在黑暗中发芽，与各种光照条件无关。SOM编码一种定位于细胞核的CCCH型锌指蛋白。由于ABA和GA代谢基因的表达变化，som突变体的ABA水平较低，GA水平升高。然而，与PIL5不同的是，SOM不调节GA不敏感和GA1阻遏物（RGA/RGA1）这两个编码GA负信号成分的DELLA基因的表达。我们的体内分析表明，PIL5通过直接结合SOM的启动子来激活其表达，这表明PIL5至少部分地通过SOM调节ABA和GA代谢基因。与这些结果一致，我们还观察到，som突变可挽救PIL5过表达株系发芽频率的降低，且这种挽救伴随着ABA和GA代谢基因的表达变化。综上所述，我们的结果表明，SOM是光敏色素信号转导途径中的一个组成部分，在种子萌发过程中调节PIL5下游的激素代谢基因。
