Chen Bing-Xian, Li Wen-Yan, Gao Yin-Tao, Chen Zhong-Jian, Zhang Wei-Na, Liu Qin-Jian, Chen Zhuang, Liu Jun
Argo-biological Gene Research Center, Guangdong Academy of Agricultural Sciences Guangzhou, China.
Front Plant Sci. 2016 Aug 12;7:1219. doi: 10.3389/fpls.2016.01219. eCollection 2016.
Seed germination is a complicated biological process that requires regulated enzymatic and non-enzymatic reactions. The action of polyamine oxidase (PAO) produces hydrogen peroxide (H2O2), which promotes dicot seed germination. However, whether and, if so, how PAOs regulate monocot seed germination via H2O2 production is unclear. Herein, we report that the coleorhiza is the main physical barrier to radicle protrusion during germination of rice seed (a monocot seed) and that it does so in a manner similar to that of dicot seed micropylar endosperm. We found that H2O2 specifically and steadily accumulated in the coleorhizae and radicles of germinating rice seeds and was accompanied by increased PAO activity as the germination percentage increased. These physiological indexes were strongly decreased in number by guazatine, a PAO inhibitor. We also identified 11 PAO homologs (OsPAO1-11) in the rice genome, which could be classified into four subfamilies (I, IIa, IIb, and III). The OsPAO genes in subfamilies I, IIa, and IIb (OsPAO1-7) encode PAOs, whereas those in subfamily III (OsPAO8-11) encode histone lysine-specific demethylases. In silico-characterized expression profiles of OsPAO1-7 and those determined by qPCR revealed that OsPAO5 is markedly upregulated in imbibed seeds compared with dry seeds and that its transcript accumulated to a higher level in embryos than in the endosperm. Moreover, its transcriptional abundance increased gradually during seed germination in water and was inhibited by 5 mM guazatine. Taken together, these results suggest that PAO-generated H2O2 is involved in coleorhiza-limited rice seed germination and that OsPAO5 expression accounts for most PAO expression and activity during rice seed germination. These findings should facilitate further study of PAOs and provide valuable information for functional validation of these proteins during seed germination of monocot cereals.
种子萌发是一个复杂的生物学过程，需要有调控的酶促反应和非酶促反应。多胺氧化酶（PAO）的作用会产生过氧化氢（H2O2），其可促进双子叶植物种子萌发。然而，PAO是否以及如何通过产生H2O2来调控单子叶植物种子萌发尚不清楚。在此，我们报道在水稻种子（一种单子叶植物种子）萌发过程中，胚根鞘是胚根突出的主要物理屏障，其作用方式类似于双子叶植物种子珠孔端胚乳。我们发现H2O2在萌发水稻种子的胚根鞘和胚根中特异性且稳定地积累，并且随着发芽率的增加，PAO活性也随之升高。这些生理指标因PAO抑制剂胍嗪而显著降低。我们还在水稻基因组中鉴定出11个PAO同源物（OsPAO1 - 11），它们可分为四个亚家族（I、IIa、IIb和III）。亚家族I、IIa和IIb中的OsPAO基因（OsPAO1 - 7）编码PAO，而亚家族III中的基因（OsPAO8 - 11）编码组蛋白赖氨酸特异性去甲基酶。对OsPAO1 - 7的电子表达谱分析以及通过qPCR测定的结果表明，与干种子相比，OsPAO5在吸胀种子中显著上调，并且其转录本在胚中的积累水平高于胚乳。此外，在水中种子萌发期间其转录丰度逐渐增加，并受到5 mM胍嗪的抑制。综上所述，这些结果表明PAO产生的H2O2参与了胚根鞘限制的水稻种子萌发，并且OsPAO5的表达占水稻种子萌发过程中大多数PAO的表达和活性。这些发现应有助于对PAO的进一步研究，并为单子叶谷类种子萌发过程中这些蛋白质的功能验证提供有价值的信息。
