Differential Expression of Methyl Jasmonate-Responsive Genes Correlates with Laticifer Vessel Proliferation in Phloem Tissue of Rubber Tree (Hevea brasiliensis)

Rubber tree (Hevea brasiliensis) is a pivotal source for natural rubber production. Polyisoprene is synthesized in laticifer vessels, which are developed from vascular cambium in the phloem area of the inner bark tissue. The transcription factors and phytohormones were reported to be involved in network regulation of plant vascular tissue differentiation. Methyl jasmonate (MeJA) was reported to act as a stimulator for laticifer vessel formation in rubber tree, but the regulatory mechanism remains largely unknown. In this study, the correlation of laticifer vessel proliferation in phloem tissue upon MeJA treatment and the MeJA-responsive gene expression was investigated. Histochemical study of the laticifer revealed the circle and diffused structure around the secondary phloem of the stem. The number of laticifer vessels was increased from the top shoot to the lower stem part. The higher average number of laticifer vessels in stems of high latex-producing clones than in low latex/high wood yield clones suggested the correlation of laticifer vessel number and latex yield potential. This study demonstrated the temporal differential expression of MeJA-responsive genes upon MeJA treatment and adjusted back to a normal level after 3 months in two high latex-producing clones. The increasing number of laticifer vessels in MeJA-treated plants confirmed the consequent effect of MeJA treatment, and the possible roles of these genes in relation with laticifer vessel proliferation are discussed. A better understanding of gene function in laticifer development would be beneficial in rubber tree improvement and exploitation.