Cao Heping, Zhang Lin, Tan Xiaofeng, Long Hongxu, Shockey Jay M
U.S. Department of Agriculture, Agricultural Research Service, Southern Regional Research Center, Commodity Utilization Research Unit, New Orleans, Louisiana, United States of America.
Key Laboratory of Cultivation and Protection for Non-Wood Forest Trees, Ministry of Education, Central South University of Forestry and Technology, Changsha, Hunan Province, People's Republic of China.
PLoS One. 2014 Feb 6;9(2):e88409. doi: 10.1371/journal.pone.0088409. eCollection 2014.
Triacylglycerols (TAG) are the major molecules of energy storage in eukaryotes. TAG are packed in subcellular structures called oil bodies or lipid droplets. Oleosins (OLE) are the major proteins in plant oil bodies. Multiple isoforms of OLE are present in plants such as tung tree (Vernicia fordii), whose seeds are rich in novel TAG with a wide range of industrial applications. The objectives of this study were to identify OLE genes, classify OLE proteins and analyze OLE gene expression in tung trees. We identified five tung tree OLE genes coding for small hydrophobic proteins. Genome-wide phylogenetic analysis and multiple sequence alignment demonstrated that the five tung OLE genes represented the five OLE subfamilies and all contained the "proline knot" motif (PX5SPX3P) shared among 65 OLE from 19 tree species, including the sequenced genomes of Prunus persica (peach), Populus trichocarpa (poplar), Ricinus communis (castor bean), Theobroma cacao (cacao) and Vitis vinifera (grapevine). Tung OLE1, OLE2 and OLE3 belong to the S type and OLE4 and OLE5 belong to the SM type of Arabidopsis OLE. TaqMan and SYBR Green qPCR methods were used to study the differential expression of OLE genes in tung tree tissues. Expression results demonstrated that 1) All five OLE genes were expressed in developing tung seeds, leaves and flowers; 2) OLE mRNA levels were much higher in seeds than leaves or flowers; 3) OLE1, OLE2 and OLE3 genes were expressed in tung seeds at much higher levels than OLE4 and OLE5 genes; 4) OLE mRNA levels rapidly increased during seed development; and 5) OLE gene expression was well-coordinated with tung oil accumulation in the seeds. These results suggest that tung OLE genes 1-3 probably play major roles in tung oil accumulation and/or oil body development. Therefore, they might be preferred targets for tung oil engineering in transgenic plants.
三酰甘油（TAG）是真核生物中能量储存的主要分子。TAG被包裹在称为油体或脂滴的亚细胞结构中。油质蛋白（OLE）是植物油体中的主要蛋白质。在油桐（Vernicia fordii）等植物中存在多种OLE同工型，其种子富含具有广泛工业应用的新型TAG。本研究的目的是鉴定油桐中的OLE基因、对OLE蛋白进行分类并分析油桐中OLE基因的表达。我们鉴定了五个编码小疏水蛋白的油桐OLE基因。全基因组系统发育分析和多序列比对表明，这五个油桐OLE基因代表了五个OLE亚家族，并且都包含来自19种树种的65个OLE共有的“脯氨酸结”基序（PX5SPX3P），包括桃（Prunus persica）、毛果杨（Populus trichocarpa）、蓖麻（Ricinus communis）、可可树（Theobroma cacao）和葡萄（Vitis vinifera）的已测序基因组。油桐OLE1、OLE2和OLE3属于拟南芥OLE的S型，OLE4和OLE5属于SM型。使用TaqMan和SYBR Green qPCR方法研究油桐组织中OLE基因的差异表达。表达结果表明：1）所有五个OLE基因在发育中的油桐种子、叶片和花中均有表达；2）种子中OLE mRNA水平远高于叶片或花；3）OLE1、OLE2和OLE3基因在油桐种子中的表达水平远高于OLE4和OLE5基因；4）种子发育过程中OLE mRNA水平迅速增加；5）OLE基因表达与种子中桐油积累良好协调。这些结果表明，油桐OLE基因1-3可能在桐油积累和/或油体发育中起主要作用。因此，它们可能是转基因植物油桐工程的首选目标。
