大戟科Lhcb基因家族的全基因组鉴定、分类与进化分析

Genome-wide identification, classification and phylogenetic analysis of Lhcb gene family in Euphorbiaceae plants

基于已公布的基因组和EST数据,研究对蓖麻、麻疯树、木薯和橡胶树4种大戟科植物的Lhcb基因家族进行系统鉴定,并在此基础上分析其基因结构与进化关系。结果表明,蓖麻、麻疯树、木薯和橡胶树分别含有10、10、13和15个Lhcb基因,分属于Lhcb1、Lhcb2、Lhcb3、Lhcb4、Lhcb5、Lhcb6、Lhcb7和Lhcb8等8个亚家族,每个亚家族包含1～4个成员不等,基因的内含子数目在0～5个之间,部分基因还存在可变剪接形式。进化分析显示,Lhcb1、Lhcb4、Lhcb5和Lhcb7亚族早于单细胞的藻类中就已产生,Lhcb3和Lhcb6亚族在光合生物向陆地进化后产生,Lhcb2亚族存在于高等植物中,Lhcb8亚族则为双子叶植物所特有;Lhcb1亚族在所分析的4种大戟科植物中均出现了基因扩增,Lhcb2和Lhcb5亚族在木薯和橡胶树中出现了扩增,而Lhcb3和Lhcb6亚族仅在橡胶树中出现了扩增。

Euphorbiaceae is a large plant family containing more than 8 000 species which are characterized with high photosynthesis and high biomass. The recently available genome sequences of some Euphorbiaceae plants such as castor bean （Ricinus communis）, physic nut （Jatropha curcas）, cassava （Manihot esculenta） and rubber tree （Hevea brasiliensis） provide an opportunity to analyze specific gene families. In this study, a genome-wide search was carried out to identify Lhcb gene family, which encodes several chlorophyll- binding proteins defined as LHCII involved in light harvesting and energy transfer to the reaction center of photosystem I1 （PSI/）, in these four Euphorbiaceae plants. As a result, a number of 10, 10, 13 and 15 Lhcb genes representing 8 subgene families named Lhcbl, Lhcb2, Lhcb3, Lhcb4, Lhcb5, Lhcb6, Lhcb7 and Lhcb8 were identified from castor bean, physic nut, cassava and rubber tree, respectively. These genes contain 0-5 introns, and some of them were found to have alternative splicing isoforms. Phylogenetic analysis suggests a early origin of subgene family Lhcb 1, Lhcb4, Lhcb5 and Lhcb7 up to unicellular algae, and subfamily Lhcb3 and Lhcb6 appear in land organisms, while subfamily Lhcb2 and Lhcbl presents only in high plants and dicotyledons, respectively. In all four analyzed Euphorbiaceae plants, gene amplification was found in subfamily Lhcbl, while gene amplification of subfamily Lhcb2 and Lhcb5 were only found in cassava and rubber tree plants. In rubber trees, amplification events also occttred in subfamily Lhcb2 and Lhcb5.