Some V PPase genes of plants are inducible and

Some V-PPase genes of plants are inducible and have essential roles in plant development and response to environmental changes [4], [36]. Stress conditions, such as cold, anoxia, chemical stimulation, wound, salt, osmotic shock and plant hormones, etc., could induce the gene PCP inhibitor and enhance the activity of V-PPase [37], [38], [39]. Our results demonstrated that JA could regulate the gene expression of Hbvp1 at both the transcription level and the translation level, and accordingly increase the hydrolytic activity of Hbvp1 on the rubber particles of H. brasiliensis. These data are consistent with other reports that the gene expression of V-PPase is regulated not only at the transcription level [40], but at the post-translational protein level [41]. The localization of the JA-responsive Hbvp1 on the rubber particles will facilitate investigation of the physiological function of JA in rubber trees. Our earlier studies suggest that JA might be an important molecule that regulates rubber biosynthesis in rubber trees [23], but the underlying mechanism is unknown. In this research, the antibody raised against Hbvp1 reduces the efficiency of incorporating [14C]IPP into rubber molecules during the rubber biosynthesis in vitro through interacting with Hbvp1 on the rubber particles; therefore, Hbvp1 might be one of the enzymes/proteins regulating rubber biosynthesis on the rubber particles. Taking these results together, one of the mechanisms by which JA regulates rubber biosynthesis might be through induction of the expression of Hbvp1 and increased Hbvp1 activity on the rubber particles, so that feedback inhibition by PPi released during rubber biosynthesis can be promptly reduced by Hbvp1 through the hydrolysis of PPi to Pi. Of course, it could not be excluded that other PPases in the latex could also be engaged in removal of PPi generated from the rubber biosynthesis. These results suggest that Hbvp1 might be a unique rubber particle membrane-associated V-PPase that is responsive to JA stimulation and is involving in regulation of the rubber biosynthesis of H. brasiliensis.
Acknowledgements
This work was supported by grants from the National Natural Science Foundation of China (Grant No.: 30260088) and the prophase research for National “973” Project of China (Grant No.: 2007CB116203). The DNA sequences of Hbvp1 and the Hbvp1 promoter were deposited in GenBank, and the accession numbers were AY 514019 and EF 198329, respectively. Author and address to whom reprint requests are to be sent: Zeng Rizhong, Rubber Research Institute, CATAS, Danzhou (571737), Hainan, PR China.
: Three structures of phosphoribosyl-ATP pyrophosphatase HisE, determined at the Mycobacterium tuberculosis () and Northeast () Structural Genomics Consortia, have been deposited recently to PDB (entries 1y6x, 1yvw and 1yxb). Inspection of these structures confirms most of the analysis presented in this paper. The only notable difference is that the two “tight” dimers in HisE tetramer are packed together at a different angle than the structurally similar “tight” dimers of the MazG protein.