Abstract

Salinity is one of the major factors negatively affecting crop productivity. WRKY transcription factors (TFs) are involved in salicylic acid (SA) mediated cellular reactive oxygen species homeostasis in response to different stresses, including salinity. Therefore, the effect of NaCl, NaCl + SA and SA treatments on different photosynthesis-related parameters and wax metabolites were studied in the Jatropha curcas WRKY (JcWRKY) overexpressing tobacco lines. JcWRKY transgenics showed improved photosynthesis rate, stomatal conductance, intercellular CO2 concentration/ambient CO2 concentration ratio (Ci/Ca ratio), electron transport rate (ETR), photosynthesis efficiency (Fv/Fm), photochemical quenching (qP), non-photochemical quenching (NPQ) and quantum yield of PSII electron transport (ΦPSII) in response to salinity stress, while exogenous SA application had subtle effect on these parameters. Alkane, the major constituent of wax showed maximum accumulation in transgenics exposed to NaCl. Other wax components like fatty alcohol, carboxylic acid and fatty acid were also higher in transgenics with NaCl + SA and SA treatments. Interestingly, the transgenics showed a higher number of open stomata in treated plants as compared to wild type (WT), indicating less perception of stress by the transgenics. Improved salinity tolerance in JcWRKY overexpressing tobacco transgenics is associated with photosynthetic efficiency and wax accumulation, mediated by efficient SA signalling. The transgenics showed differential regulation of genes related to photosynthesis (NtCab40, NtLhcb5 and NtRca1), wax accumulation (NtWIN1) and stomatal regulation (NtMUTE, NtMYB-like, NtNCED3-2 and NtPIF3). The present study indicates that JcWRKY is a potential TF facilitating improved photosynthesis with the wax metabolic co-ordination in transgenics during stress.

Highlights

  • Salinity is one of the major factors negatively affecting crop productivity

  • The intercellular CO2 concentration/ambient CO2 concentration (Ci/Ca) ratio was lower in transgenics with water, salicylic acid (SA) and NaCl + SA treatments, a drastic increase of 170% was observed with NaCl stress as compared to wild type (WT) (Fig. 1E)

  • The transgenics showed improved electron transport rate (ETR) by 5.3%, 23.36% with water and NaCl, respectively, while in NaCl + SA stress, ETR got reduced by 2.6% as compared to WT (Fig. 1F)

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Summary

Introduction

Salinity is one of the major factors negatively affecting crop productivity. WRKY transcription factors (TFs) are involved in salicylic acid (SA) mediated cellular reactive oxygen species homeostasis in response to different stresses, including salinity. The Jatropha curcas WRKY (JcWRKY) overexpressing tobacco transgenics have earlier shown improved salinity tolerance via co-ordination of SA signalling and ROS homeostasis[22] and in the present study, we aimed to elucidate the role of JcWRKY TF in regulation of photosynthesis parameters, leaf epicuticular wax accumulation, leaf stomata density and gene expression analysis in transgenics during salinity, SA and combinatorial stress (NaCl + SA). To our knowledge, this is the first report of JcWRKY showing the interaction between photosynthesis and wax accumulation in transgenics towards improved salinity tolerance

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