GenomeWide Identification and Analysis of PMK Gene Family of Four Euphorbiaceae Plants

The 5-phosphomevalonate kinase (PMK) is an essential enzyme in mevalonate (MVA) pathway that catalyzes the reversible phosphorylation of mevalonate 5-phosphate (MVAP) to form mevalonate-5-diphosphate (MVAPP) in the presence of ATP and divalent ion such as Mg2+. Based on the released genome and EST data, a genomewide search was carried out for the first time to identify PMK gene family of four Euphorbiaceae plant species i.e., castor bean (Ricinus communis), physic nut (Jatropha curcas), cassava (Manihot esculenta) and rubber tree (Hevea brasiliensis), and subsequently, the gene structure and evolutionary relationship were also analyzed. As a result, a number of 1, 1, 1 and 2 PMK gene(s) were identified from castor bean, physic nut, cassava and rubber tree, respectively, and all of them contained 9 introns. Homology analyses suggested that PMK genes can be divided into two types, and type I is widely distributed in plants, some archaea, eubacteria and fungi, while type II is specific to animals. Although PMK genes were identified in most green plants, no homologous genes were found in unicellular green algae. In most genome sequenced plants including castor bean, physic nut and cassava, a single copy of PMK gene was found, however, in rubber tree plant, two copies were identified just like that in maize (Zea mays) and poplar (Populus trichocarpa). In castor bean, digital expression profiling suggested that in five examined tissues such as leaf, flower, II/III stage endosperm, V/VI stage endosperm and seed, RcPMK was expressed strongly in II/III stage endosperm, moderately in leaf, seed and flower, weakly in V/VI stage endosperm.