Mechanisms and Genes Related to Rice Root Hydraulics under Drought

In plant response to drought, root functional parameters (i.e. hydraulics) likely complement root architecture, but have been explored to a lesser extent. In this study, we investigated rice root hydraulics through a combination of field physiological and gene expression approaches. This work is a continuation of our previous research that indicated higher sap bleeding rates in drought susceptible genotypes, which was consistent across soil moisture and ambient conditions and which was correlated with leaf osmotic potential. In this study, 20 diverse rice genotypes were grown in lowland conditions under vegetative stage drought stress. Root crowns were excavated and only healthy root tips from within the root crown were sampled for root osmotic potential and RNAseq analyses. We observed inter-relationships among sap bleeding rate, leaf osmotic potential, sap K⁺ concentration, and root osmotic potential. Roots showed earlier response to stress than leaves, as reflected by osmotic potential of those tissues as well as gene expression patterns between roots and shoots. Notably, several aquaporins were upregulated in roots under drought stress confirming previous observations of those genes in greenhouse-grown root tips. These results will help to pinpoint specific rice root hydraulic traits that could be targeted for improvement, especially regarding their contribution to drought response.