Rahman Hafizur, Xu You-Ping, Zhang Xuan-Rui, Cai Xin-Zhong
Institute of Biotechnology, College of Agriculture and Biotechnology, Zhejiang University Hangzhou, China.
Center of Analysis and Measurement, Zhejiang University Hangzhou, China.
Front Plant Sci. 2016 May 4;7:581. doi: 10.3389/fpls.2016.00581. eCollection 2016.
Calmodulin-binding transcription activators (CAMTAs) play important roles in various plant biological processes including disease resistance and abiotic stress tolerance. Oilseed rape (Brassica napus L.) is one of the most important oil-producing crops worldwide. To date, compositon of CAMTAs in genomes of Brassica species and role of CAMTAs in resistance to the devastating necrotrophic fungal pathogen Sclerotinia sclerotiorum are still unknown. In this study, 18 CAMTA genes were identified in oilseed rape genome through bioinformatics analyses, which were inherited from the nine copies each in its progenitors Brassica rapa and Brassica oleracea and represented the highest number of CAMTAs in a given plant species identified so far. Gene structure, protein domain organization and phylogentic analyses showed that the oilseed rape CAMTAs were structurally similar and clustered into three major groups as other plant CAMTAs, but had expanded subgroups CAMTA3 and CAMTA4 genes uniquely in rosids species occurring before formation of oilseed rape. A large number of stress response-related cis-elements existed in the 1.5 kb promoter regions of the BnCAMTA genes. BnCAMTA genes were expressed differentially in various organs and in response to treatments with plant hormones and the toxin oxalic acid (OA) secreted by S. sclerotiorum as well as the pathogen inoculation. Remarkably, the expression of BnCAMTA3A1 and BnCAMTA3C1 was drastically induced in early phase of S. sclerotiorum infection, indicating their potential role in the interactions between oilseed rape and S. sclerotiorum. Furthermore, inoculation analyses using Arabidopsis camta mutants demonstrated that Atcamta3 mutant plants exhibited significantly smaller disease lesions than wild-type and other Atcamta mutant plants. In addition, compared with wild-type plants, Atcamta3 plants accumulated obviously more hydrogen peroxide in response to the PAMP chitin and exhibited much higher expression of the CGCG-box-containing genes BAK1 and JIN1, which are essential to the PAMP triggered immunity (PTI) and/or plant resistance to pathogens including S. sclerotiorum. Our results revealed that CAMTA3 negatively regulated PTI probably by directly targeting BAK1 and it also negatively regulated plant defense through suppressing JA signaling pathway probably via directly targeting JIN1.
钙调蛋白结合转录激活因子（CAMTAs）在包括抗病性和非生物胁迫耐受性在内的各种植物生物学过程中发挥着重要作用。油菜（Brassica napus L.）是全球最重要的油料作物之一。迄今为止，甘蓝型油菜物种基因组中CAMTAs的组成以及CAMTAs在抵抗毁灭性坏死营养型真菌病原体核盘菌（Sclerotinia sclerotiorum）中的作用仍然未知。在本研究中，通过生物信息学分析在油菜基因组中鉴定出18个CAMTA基因，这些基因分别从其祖先白菜（Brassica rapa）和甘蓝（Brassica oleracea）中的9个拷贝遗传而来，代表了迄今为止在特定植物物种中鉴定出的最多数量的CAMTAs。基因结构、蛋白质结构域组织和系统发育分析表明，油菜CAMTAs在结构上与其他植物CAMTAs相似，并聚类为三个主要组，但在油菜形成之前出现的蔷薇类物种中独特地扩展了亚组CAMTA3和CAMTA4基因。BnCAMTA基因的1.5 kb启动子区域存在大量与胁迫反应相关的顺式元件。BnCAMTA基因在各个器官中差异表达，并响应植物激素处理以及核盘菌分泌的毒素草酸（OA）以及病原体接种。值得注意的是，BnCAMTA3A1和BnCAMTA3C1的表达在核盘菌感染的早期阶段被显著诱导，表明它们在油菜与核盘菌相互作用中的潜在作用。此外，使用拟南芥camta突变体的接种分析表明，Atcamta3突变体植物表现出比野生型和其他Atcamta突变体植物明显更小的病斑。此外，与野生型植物相比，Atcamta3植物在响应PAMP几丁质时积累了明显更多的过氧化氢，并且表现出含CGCG-box的基因BAK1和JIN1的更高表达，这些基因对于PAMP触发的免疫（PTI）和/或植物对包括核盘菌在内的病原体的抗性至关重要。我们的结果表明，CAMTA3可能通过直接靶向BAK1负向调节PTI，并且它也可能通过直接靶向JIN1抑制JA信号通路来负向调节植物防御。
