Differing Drought Response Strategies Revealed by Natural Variation in Metabolite and Abscisic Acid Levels among Arabidopsis thaliana Accessions

Natural variation among Arabidopsis thaliana accessions can reveal genetic mechanisms of environmental adaptation, including adaptation to environments differing in the timing, severity and frequency of drought.  We found substantial natural variation in levels of the stress hormone Abscisic Acid (ABA) and the protective metabolite proline after exposure to low water potential.  Much of the variation in proline level was caused by intron polymorphisms which led to alternative splicing and production of a non-functional transcript from the gene encoding the key proline synthesis enzyme Δ¹-pyrroline-5-carboxylate synthetatse1 (P5CS1; Kesari et al., 2012 PNAS 109: 9197).  Correlation of P5CS1 splicing and proline accumulation with climate patterns indicated that accessions from drier climates have lower proline accumulation and may have evolved alternative metabolic strategies to cope with water limitation.  Consistent with this hypothesis, we found that the low proline accession Shahdara (Sha) was not low water potential sensitive like p5cs1 knockout mutants in the Col background.  Also, Sha had extensive metabolite and gene expression differences compared to the high proline accession Landsberg erecta that were indicative of a different stress response strategy (Sharma et al., 2013 Plant Cell & Environment: doi: 10.1111/pce.12032).  We also found several-fold variation among accessions in stress-induced ABA accumulation and are using QTL mapping and analysis of candidate genes to understand the basis for these differences in ABA level.