Study On Ethylene Response Characteristics Of HbSUT3in Different Hevea Clones And Its Molecular Evolution

Natural rubber (cis-1,4-polyisoprene) was used in national defense construction and all fields of national economy with physical properties superior to synthetic rubber. By now, the production of nature rubber is less than one fifth of consumption in our country. Therefore, it is important to improve the yield of natural rubber in our country. It is found that a medium scale gene family of sucrose transporter (SUT) plays an important role in rubber yield through regulation of latex production. According to previous study of different HbSUT that the sucrose transporter HbSUT3plays an active role in sucrose loading to laticifer to improve rubber productivity, and these results provide a breakthrough for the molecular mechanisms in ethylene stimulation of latex production. Therefore, the study on functional expression profiles of HbSUT has the vital significance to clarify the molecular mechanisms of rubber high-yield. In our study, we analyze the expression profiles of HbSUT, especially HbSUT3, using three different metabolic level Hevea clones with ethylene stimulation. At the same time, we also study on the genetic evolution of HbSUT3to investigate the correlation between molecular evolution and latex yield. The main results are as follows:1. Comprehensive analysis the correlation between expression of HbSUT3and latex production in RY8-79and PR107, we found that, HbSUT3is always up-regulate by ethylene stimulation which significantly increase production of latex in low metabolic level Hevea clones, and the same results occurs in high metabolic level Hevea clones in their low metabolism period. But there is no response and slightly down-regulate by ethylene stimulation in their high metabolism period of high metabolic level Hevea clones, and the same trend occurs in latex production. This result shows that ethylene regulates the expression of HbSUT3to stimulate the latex production. Finally we draw the conclusion that HbSUT3is the key HbSUT which influences the production of latex by ethylene stimulation.2. The results of the study on ethylene stimulation show that HbSUT3is the most sensitive HbSUT by ethylene stimulation in latex and bark. HbSUT3is always the main up-regulate gene (50-fold) than other HbSUT (less than6-fold) by ethylene stimulation in latex and bark from three clones.3. By the study on expression patterns of HbSUT in latex and bark from RY8-79(high metabolic level), RY7-33-97(medium metabolic level) and PR107(low metabolic level) Hevea clones, we found that:HbSUT3has the highest basal expression in all Hevea clones with any metabolic level, and the order from high to low of three clones is RY8-79、 RY7-33-97and PR107. Research also shows that:the expression pattern of HbSUT3ishigher expression in latex than bark from the same clone. These results convey important information that HbSUT3is the main expression HbSUT in latex, and the latex production is positively correlated with the expression of HbSUT3.4. The genomic clones of all HbSUT3and its homologs contained four exons and three introns, and all had a cDNA coding sequence of1608bp;the ratios of transitions to transversions between different samples were lower than2.0, and the values of Ks were generally larger that those of Ka for maximum; phylogenetic tree showed that high-yielding H.brasiliensis samples tended to cluster together, but samples of several Hevea species can also be grouped together. HbSUT3and its homologs are evolutionally conservative, and the molecular evolution of HbSUT3has correlation with latex yield. In addition, the evolutionary analyses provide molecular evidence for the idea that the genus Hevea can be considered as species complex.The results of this paper further proof that HbSUT3is the key SUT gene participating in latex yield formation and influencing the increase effect by ethylene stimulation, and it helps to further reveal the molecular mechanism of ethylene stimulation in latex production, and providing theoretical guidance and the target genes for directional molecular improvement of Hevea clones.