Ye Lin-Shan, Zhang Qin, Pan Hui, Huang Chao, Yang Zhong-Nan, Yu Qing-Bo
College of Life and Environmental Sciences, Shanghai Normal University, Shanghai 200234, China.
College of Tourism, Shanghai Normal University, Shanghai 200234, China.
Physiol Plant. 2017 Nov;161(3):414-430. doi: 10.1111/ppl.12603. Epub 2017 Aug 4.
In higher plants, chloroplasts carry out many important functions, and normal chloroplast development is required for embryogenesis. Numerous chloroplast-targeted proteins involved in embryogenesis have been identified. Nevertheless, their functions remain unclear. In this study, a chloroplast-localized protein, EMB2738, was reported to be involved in Arabidopsis embryogenesis. EMB2738 knockout led to defective embryos, and the embryo development in emb2738 was interrupted after the globular stage. Complementation experiments identified the AT3G12080 locus as EMB2738. Cellular observation indicated that severely impaired chloroplast development was observed in these aborted embryos. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) analysis showed that chloroplast-encoded photosynthetic genes, which are transcribed by plastid-encoded RNA polymerase (PEP), are predominantly decreased in defective embryogenesis, compared with those in the wild-type. In contrast, genes encoding PEP core subunits, which are transcribed by nucleus-encoded RNA polymerase (NEP), were increased. These results suggested that the knockout of EMB2738 strongly blocked chloroplast-encoded photosynthesis gene expression in embryos. Silencing of the EMB2738 orthologue in tobacco through a virus-induced genome silencing technique resulted in an albinism phenotype, vacuolated chloroplasts and decreased PEP-dependent plastid transcription. These results suggested that NtEMB2738 might be involved in plastid gene expression. Nevertheless, genetic analysis showed that the NtEMB2738 coding sequence could not fully rescue the defective embryogenesis of the emb2738 mutant, which suggested functional divergence between NtEMB2738 and EMB2738 in embryogenesis. Taken together, these results indicated that both EMB2738 and NtEMB2738 are involved in the expression of plastid genes in higher plants, and there is a functional divergence between NtEMB2738 and EMB2738 in embryogenesis.
在高等植物中，叶绿体执行许多重要功能，胚胎发生需要正常的叶绿体发育。已鉴定出许多参与胚胎发生的叶绿体靶向蛋白。然而，它们的功能仍不清楚。在本研究中，据报道一种叶绿体定位蛋白EMB2738参与拟南芥胚胎发生。EMB2738基因敲除导致胚胎缺陷，emb2738中的胚胎发育在球形期后中断。互补实验确定AT3G12080位点为EMB2738。细胞观察表明，在这些败育胚胎中观察到叶绿体发育严重受损。定量逆转录-聚合酶链反应（qRT-PCR）分析表明，与野生型相比，由质体编码的RNA聚合酶（PEP）转录的叶绿体编码光合基因在缺陷胚胎发生中主要减少。相反，由核编码的RNA聚合酶（NEP）转录的编码PEP核心亚基的基因增加。这些结果表明，EMB2738基因敲除强烈阻断了胚胎中叶绿体编码的光合作用基因表达。通过病毒诱导的基因组沉默技术使烟草中的EMB2738直系同源基因沉默，导致白化病表型、液泡化叶绿体和PEP依赖的质体转录减少。这些结果表明NtEMB2738可能参与质体基因表达。然而，遗传分析表明，NtEMB2738编码序列不能完全挽救emb2738突变体的缺陷胚胎发生，这表明NtEMB2738和EMB2738在胚胎发生中存在功能差异。综上所述，这些结果表明EMB2738和NtEMB2738都参与高等植物质体基因的表达，并且NtEMB2738和EMB2738在胚胎发生中存在功能差异。
