Abstract
Among thiols oxidoreductases, class III CC-type glutaredoxins (also called ROXYs) are land plant specific, and their evolutionary history is highly dynamic. Angiosperms encode many isoforms classified into five subgroups (A, A, B, B, B) that probably evolved from five common ancestral ROXYs, with higher evolutionary dynamics in B compared to other subgroups. ROXYs participate in the control of proper plant development and reproduction, and are important regulators of plant responses to biotic and abiotic stresses. Early drought stress is an important constraint in agrosystems in the Sahel where pearl millet was domesticated. Furthermore, we show that increased pearl millet primary root growth is correlated with increased early water stress tolerance in field conditions. Using genome-wide association study (GWAS) and quantitative trait loci (QTL) approaches, we identified genomic regions controlling key root traits correlated with increased early water stress tolerance in field conditions in pearl millet. Combining gene expression data, re-sequencing and re-annotation of one of these genomic regions, we identified the glutaredoxin-encoding gene PgROXY19 as the candidate stress resilience root growth regulator. Functional characterization of its closest Arabidopsis thaliana homolog AtROXY19 revealed a novel role for this glutaredoxin gene clade in regulating cell elongation. Therefore, our study suggests a conserved function for ROXY19 in conferring root cell elongation and enhancing resilience of pearl millet to drought stress in its Sahelian environment.