Abstract
Osmotin-like proteins (OLPs), of PR-5 family, mediate defense against abiotic, and biotic stresses in plants. Overexpression in sesame of an OLP gene (SindOLP), enhanced tolerance against drought, salinity, oxidative stress, and the charcoal rot pathogen. SindOLP was expressed in all parts and localized to the cytosol. The transgenic plants recovered after prolonged drought and salinity stress, showing less electrolyte leakage, more water content, longer roots, and smaller stomatal aperture compared to control plants. There was an increase in osmolytes, ROS-scavenging enzymes, chlorophyll content, proline, secondary metabolites, and reduced lipid peroxidation in the transgenic sesame under multiple stresses. The OLP gene imparted increased tolerance through the increased expression of three genes coding for ROS scavenging enzymes and five defense-related marker genes functioning in the JA/ET and SA pathways, namely Si-Apetala2, Si-Ethylene-responsive factor, Si-Defensin, Si-Chitinase, and Si-Thaumatin-like protein were monitored. The transgenic lines showed greater survival under different stresses compared to control through the integrated activation of multiple components of the defense signaling cascade. This is the first report of transgenic sesame and first of any study done on defense-related genes in sesame. This is also the first attempt at understanding the molecular mechanism underlying multi-stress tolerance imparted by an OLP.
Highlights
Combinations of abiotic and biotic stresses, instead of individual ones, create a realistic threat to crop cultivation throughout the world
Thirteen T0 lines having a single copy of SindOLP(detected by q-RT-PCR) were selected (Supplementary Figure S1, Supplementary Table S1)
Twenty to Twenty-five seedlings of each group were again checked for Kanamycin resistance and for segregation of SindOLP sequence through PCR
Summary
Combinations of abiotic and biotic stresses, instead of individual ones, create a realistic threat to crop cultivation throughout the world. The concurrent presence of an abiotic stress either aggravates or impedes the effect of infection by a pathogen, thereby rendering a plant susceptible or tolerant against the combined stresses (Ramegowda and Senthil-Kumar, 2015). Stress signaling in plants in response to abiotic and biotic factors can induce separate and overlapping sets of genes, leading to the expression of distinct as well as common components (Zhu et al, 2014; Mellacheruvu et al, 2016) These separate pathways show nodal points where they converge and cross-talk to optimize the various defense responses (Xiao et al, 2013), resulting in shared stress mitigation strategy by combined morpho-physiological processes as well as by molecular responses (Pandey et al, 2015). Genes such as those coding for Osmotins or Osmotin-like proteins that impart abiotic as well as biotic stress tolerance present an opportunity to study the mechanism underlying tolerance to dual stresses
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