Adaptive growth homeostasis in response to drought in Iberian Arabidopsis accessions

ABSTRACT

Plants respond to environmental fluctuations through plastic phenotypic shifts. Whether a plastic response upon environmental variability is adaptive or not has been subject to debate. Using a set of Iberian Arabidopsis accessions, we quantified an interplay between passive plastic reductions in leaf areas that we found typical of accessions from productive environments and homeostatic leaf areas responses to drought typified by accessions originating from unproductive environments. Results from Genome-Wide Association Studies (GWAS) and Transcriptome Wide Association Studies (TWAS) highlight the role of auxin-related processes and, in particular, the possible role of the SMALL AUXIN UP RNA 26 (SAUR26) gene in the regulation of the observed plastic responses. Homeostatic responses in leaf area potential following drought were typical of accessions with lower leaf area potential under well-watered conditions. Transcripts that were negatively associated with leaf area potential and positively associated with homeostatic and positive leaf area plasticity following drought showed functional enrichment in ion transport processes. We hypothesized that the contrasting plastic and homeostatic responses in leaf area potential were associated with differential intrinsic water use efficiency (WUE_i). We confirmed this relationship in a metanalysis conducted using previously published δ¹³C measurements. Our results highlight the adaptive role of homeostatic leaf area response to water depletion arising from increased WUE_i. The concerted utilization of Genome-Wide Association Studies (GWAS), Transcriptome Wide Association Studies (TWAS), and expression Genome-Wide Association Studies (eGWAS) allows integration of phenotype, genotype, and transcript abundance to identify both “plasticity genes” and “homeostasis genes” associated with drought stress responses.