|Kottapalli, Kameswara Rao|
Submitted to: Plant Cell and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/8/2008
Publication Date: 12/5/2008
Citation: Kottapalli, K., Rakwal, R., Shibato, J., Burow, G.B., Burke, J.J., Puppala, N., Payton, P.R., Burow, M. 2008. Physiology and proteomics of the water-deficit stress response in three contrasting peanut genotypes. Plant, Cell and Environment. 32(4):380-407. Interpretive Summary: Approximately 25% of peanut production is in the semi-arid southwestern U.S. Despite peanut being drought adaptive, increasing acreage, competition from urban water usage, and depleting water resources like the Ogallala Aquifer are threatening sustainable crop production. Water-deficit stress results in variable yield losses depending on the crop stage, duration of stress, and intensity. Annually, losses from drought exceed $500 million and it is estimated that roughly 50% of the loss in productivity could be recovered through genetic improvement for drought tolerance with a benefit cost ratio of 5:2. Despite the agronomic and economic importance of drought, very little is known about the molecular mechanisms in peanuts. Most of the drought molecular responses studied to date consider transcriptional modification of gene expression and the identification of candidate genes for engineering stress tolerance. However, cellular processes are also driven by post-transcriptional processes including protein-protein interactions, post-translational protein modifications, making accurate prediction of enzyme activities by gene expression studies alone difficult. Proteins on the other hand are directly associated with function and proteomic approaches are being applied increasingly to address various biochemical and physiological questions. In an attempt to identify drought tolerant material in the existing genetic stocks and understand the molecular mechanism of drought tolerance in peanuts, we have screened seventy uniform accessions from the U.S. peanut mini-core collection along with seven peanut cultivars and selected the twenty best accessions for drought screening. A novel bioassay, combined with physiological parameters such as water use efficiency and specific leaf area, identified two contrasting mini-core accessions for water deficit-stress tolerance. Aproteomics approach was utilized to examine the response to water-deficit stress under controlled conditions. A total of 101 differentially expressed proteins were identified under drought stress in the leaves of selected accessions using both one- and two-dimensional gel eletrophoresis coupled with LC-MS/MS and MALDI-TOF. We identified key enzymes of lipid biosynthetic pathway involved in cuticular wax formation, lignification, and jasmonic acid signaling. It is likely that some of these differential proteins may be associated with drought tolearance in peanuts. We propose a hypothetical drought tolerance mechanism with physiologically important candidate proteins in peanuts.
Technical Abstract: Peanut (Arachis hypogaea L.) accessions from the US mini core collection were analyzed for differentially expressed leaf proteins during reproductive stage under water-deficit stress. Accessions showing tolerant and susceptible responses to stress were selected based on a bioassay involving chlorophyll fluorescence yield under elevated respiratory demand, water use efficiency and specific leaf area. One- and two-dimensional gel electrophoresis (1- and 2-DGE) was performed on leaf soluble protein extracts of selected tolerant and susceptible accessions and a moderately tolerant cultivar. One- dimensional gel immunoblotting revealed significant induction of small heat shock proteins during water-stress to safeguard the photosystem II (PSII) machinery. A total of 22 and 79 protein bands/spots from 1- D and 2- D gels, respectively, were analyzed by matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF MS) and by MS/MS analysis, and 48 non-redundant proteins were identified. Acetyl-CoA carboxylase, a key enzyme of lipid biosynthesis, was induced only in the tolerant accession indicating a novel fatty acid mediated mechanism of drought tolerance. Induction of lipoxygenase an enzyme of jasmonic acid biosynthesis along with aldolases, myo-inositol, and lectins primarily aid in inter and intra cellular drought signaling. Photosynthetic proteins were suppressed in tolerant accession suggesting a decline in carbon assimilation as a “water economy measure” during stress. This study, for the first time demonstrates that leaf proteins involved in a variety of cellular functions like cell wall strengthening, signal transduction, energy metabolism, cellular detoxification, and novel gene regulation impinge on the molecular mechanism of drought tolerance in peanut plants. Some of these identified proteins upon elaborate functional characterization should strengthen the resources of drought breeders for peanut crop improvement.