Gene expression pattern in response to wounding, methyl jasmonate and ethylene in the bark of Hevea brasiliensis

Natural rubber production in Hevea brasiliensis is determined by both tapping and ethephon frequencies. It is affected by a complex physiological disorder called tapping panel dryness. This syndrome is likely to be induced by environmental and latex harvesting stresses. Defence responses, including rubber biosynthesis, are dramatically mediated by wounding, jasmonate and ethylene (ET), among other factors. Using real-time RT-PCR, the effects of wounding, methyl jasmonate (MeJA) and ET on the relative transcript abundance of a set of 25 genes involved in their signalling and metabolic pathways were studied in the bark of 3-month-old epicormic shoots. Temporal regulation was found for 9 out of 25 genes. Wounding treatment regulated the transcript abundance of 10 genes. Wounding-specific regulation was noted for the HbMAPK, HbBTF3b, HbCAS1, HbLTPP and HbPLD genes. MeJA treatment regulated the transcript abundance of nine genes. Of these, the HbMYB, HbCAS2, HbCIPK and HbChi genes were shown to be specifically MeJA inducible. ET response was accompanied by regulation of the transcript abundance of eight genes, and six genes, HbETR2, HbEIN2, HbEIN3, HbCaM, HbPIP1 and HbQM, were specifically regulated by ET treatment. Additionally, the transcript level of the HbGP and HbACR genes was enhanced by all three treatments simultaneously. Overall, a large number of genes were found to be regulated 4 h after the treatments were applied. This study nevertheless revealed some jasmonic acid-independent wound signalling pathways in H. brasiliensis, provided a general characterization of signalling pathways and will serve as a new base from which to launch advanced studies of the network of pathways operating in H. brasiliensis.