Abstract
Tolerance of recurrent mechanical wounding and exogenous ethylene is a feature of the rubber tree. Latex harvesting involves tapping of the tree bark and ethephon is applied to increase latex flow. Ethylene is an essential element in controlling latex production. The ethylene signalling pathway leads to the activation of Ethylene Response Factor (ERF) transcription factors. This family has been identified in Hevea brasiliensis. This study set out to understand the regulation of ERF genes during latex harvesting in relation to abiotic stress and hormonal treatments. Analyses of the relative transcript abundance were carried out for 35 HbERF genes in latex, in bark from mature trees and in leaves from juvenile plants under multiple abiotic stresses. Twenty-one HbERF genes were regulated by harvesting stress in laticifers, revealing an overrepresentation of genes in group IX. Transcripts of three HbERF-IX genes from HbERF-IXc4, HbERF-IXc5 and HbERF-IXc6 were dramatically accumulated by combining wounding, methyl jasmonate and ethylene treatments. When an ethylene inhibitor was used, the transcript accumulation for these three genes was halted, showing ethylene-dependent induction. Subcellular localization and transactivation experiments confirmed that several members of HbERF-IX are activator-type transcription factors. This study suggested that latex harvesting induces mechanisms developed for the response to abiotic stress. These mechanisms probably depend on various hormonal signalling pathways. Several members of HbERF-IX could be essential integrators of complex hormonal signalling pathways in Hevea.
Highlights
Latex, a rubber-containing cytoplasm, is harvested by tapping soft bark tissues of Hevea brasiliensis
This study suggested that latex harvesting induces mechanisms developed for the response to abiotic stress
Specific amplification of 47 of the 114 Hevea genes from the AP2/Ethylene Response Factor (ERF) superfamily including AP2, ERF and RAV genes was validated by sequencing [18].The relative transcript abundance for these 47 genes was analysed in latex and bark of 1-year-old tapped trees treated or not by ethephon (Fig 1)
Summary
A rubber-containing cytoplasm, is harvested by tapping soft bark tissues of Hevea brasiliensis. Latex production depends on the flow and regeneration of latex between two tappings. An ethylene releaser, is applied to the tapping panel to stimulate latex production. Ethephon application induces several biochemical changes in laticifers, such as sucrose loading. The Institut Français du Caoutchouc (IFC), and the Michelin, Socfinco and Société Internationale de PLantations d'Hévéas (SIPH)companies provided a 18-month scholarship to Mr Riza-Arief Putranto, and funded all bench fees for experiments related to this paper. CATAS and the Beijing Institute of Genomics provided access to the Hevea genome sequence. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. The IFC agreed to publish this manuscript
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