Transcriptional responses of laticifer-specific genes to phytohormones in a suspension-cultured cell line derived from petioles of Hevea Brasiliensis

Hevea brasiliensis is the key source of latex for commercial natural rubber production. Genetic improvement of H. brasiliensis is required to enhance natural rubber production, although the biosynthetic mechanism has not been fully elucidated. In this study, we established a cell suspension culture from petiole explants of H. brasiliensis clone RRIM 600 for basic research on the biosynthesis of natural rubber. Calli were induced from petiole explants on callus induction medium supplemented with 2 mg l^-1 2,4-dichlorophenoxyacetic acid (2,4-d) and 0.05 mg l^-1 6-benzylaminopurine (BA). Then, the calli were suspension cultured in MS basal medium supplemented with 2 mg l^-1 2,4-d and 2 mg l^-1 BA. Although transcripts of some laticifer-specific genes were detected in the cultured cells, their levels were much lower than those in the other laticifer-containing tissues. Additionally, there was no detectable activity of rubber transferase in this cell line. The laticifer-specific genes in the cell line showed transcriptional responses to phytohormone treatments. Among them, up-regulations of Rubber Elongation Factor by the ethophon treatment were concordant with those in laticifers, suggesting that these cells retained at least some of the cytochemical properties of laticifers. The cell line established in this study could be useful for biochemical and molecular studies on natural rubber biosynthesis.