Résumé
Seedling root traits impact plant establishment under challenging
environments. Pearl millet is one of the most heat- and drought-tolerant
cereal crops that provides a vital food source across the sub-Saharan
Sahel region. Pearl millet’s early root system features a single
fast-growing primary root which we hypothesize is an adaptation to the
Sahelian climate. Using crop modelling, we demonstrate that 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. Genetics including GWAS and QTL approaches
identify genomic regions controlling this key root trait. Combining gene
expression data, re-sequencing and re-annotation of one of these genomic
regions identified a glutaredoxin-encoding gene PgGRXC9 as the
candidate stress resilience root growth regulator. Functional
characterization of its closest Arabidopsis
homolog AtROXY19 revealed a novel role for this
glutaredoxin (GRX) gene clade in regulating cell elongation. In summary,
our study suggests a conserved function for GRX genes in conferring root
cell elongation and enhancing resilience of pearl millet to its Sahelian
environment.