A highly efficient callus model to study gene functions: HbSRPP1 may play a role in the elongation of cis-1,4-polyisoprene in the rubber tree

Natural rubber (NR) is synthesized in the laticifer cells of the rubber tree by a series of enzymes located on the membrane of the rubber particles (RPs). Traditional methods for function studies of NR biosynthesis-related genes are of low efficiency due to difficulties in obtaining transgenic plants and years of research cycle. We established a callus model for function studies without the need to regenerate transgenic plants. The callus of the rubber tree differentiated into laticifer cells efficiently with the induction by jasmonic acid, and RPs were observed by histochemical analysis. The rubber isolated from the callus was cis-1,4-polyisoprene with molecular weights similar to the rubber tapped from the tree. Laticifer-specific expression vectors of GUS and EGFP was constructed, and target genes can be easily inserted between the promoter and the reporter genes by Nimble cloning. HbSRPP1 gene was used as an example to test the efficiency of the callus model. HbSRPP1 cDNA was cloned in the laticifer-specific and EGFP-tagged expression vector, and transformed into the callus. The expression of HbSRPP1 gene was significantly up-regulated in the transgenic callus, and EGFP-tagged HbSRPP1 protein was successfully produced and dispatched onto the RPs. As a consequence, the content and molecular weight of the rubber were increased significantly in the transgenic callus, indicating that HbSRPP1 may play a role in the elongation of the cis-1,4-polyisoprene chain of the rubber and thus increase the rubber content. These results indicate that the callus can serve as an effective model for studying biological functions of genes that are related to laticifer development and rubber biosynthesis without the need to regenerate transgenic plants, and thus may accelerate functional genomics research and molecular breeding in the rubber tree. • The callus of the rubber tree synthesizes rubber similar to that of the rubber tree. • A rapid and highly efficient callus model was established for gene function studies. • An EGFP-tagged expression vector was constructed to carry target genes into the callus cells. • The function of HbSRPP1 was revealed for the first time by using the callus model. • HbSRPP1 locates on the rubber particles and elongates cis-1,4-polyisoprene.