[Over-expression of OsPSK3 increases chlorophyll content of leaves in rice]

Phytosulfokine (PSK) is a newly discovered plant hormone, which can promote cell division and induce cell differentiation. It has 7 members in rice genome. So far, how the OsPSK functions and regulates in vivo is remaining unclear. In this study, we first did structural comparison and phylogenetic analysis of the 7-OsPSK-gene family via bioinformatics. Based on the phylogenetic analysis of the PSK genes in rice and Arabidopsis, we draw the conclusion that the formation of two paralogous PSK genes from the ancestral one was earlier than the monocotyledon-dicotyledon divergence; in addition, OsPSK1 and the rest OsPSK2-OsPSK7 stemmed from two different ancestors. Interrogating expression profiles of each OsPSK family member in different tissues showed different genes with different expression patterns. By means of the method of particle bombardment, we developed an OsPSK3 transgenic line, and further put much effort on studying rice growth under OsPSK3 overexpression background. It showed that the OsPSK3 overexpression line, OsPSK3ox increased OsPSK3 expression about 40% over the wild type, and presented obvious growth vigor with more fibrous roots and more root hairs at seedling stage. Plant height of OsPSK3ox-1 was higher from seedling to the full ripe stage. Notably in chlorophyll content of leaves, OsPSK3ox plants increased 2.3 times over that of the wild type.