Characterizing drought response strategies in diverse Asian rice varieties

Abstract

Drought events are being exacerbated by climate change and result in the reduced growth, yield, and survival of crops. Rice, a staple crop in the diets of nearly half of the global population, is a semi-aquatic plant that is extremely sensitive to drought. However, the natural and artificial selection of rice across varying ecological regions and climates worldwide has resulted in the adaptation of different cultivated varieties (cultivars) of rice to diverse environmental conditions, leading to variable drought resistance capabilities and differential investments into distinct drought response strategies, such as increased root growth or early maturation, across cultivars. These response strategies can be largely grouped into three categories: drought tolerance, drought avoidance, and drought escape. Rice drought response, however, is a complex, multigenic trait involving many converging molecular pathways that regulate plant structure and function. As a result, much about the coordinated internal networks controlling rice drought responses remains unknown. In this study, growth and gas exchange parameters were compared across 17 regionally distinct Asian rice (Oryza sativa) cultivars grown in either well-watered (3 g H2O/g dry soil) or growth-limiting drought (1 g H2O/g dry soil) soil conditions to screen for drought response. The chlorophyll content and relative transcript abundance of target genes (OsABA2, OsADF3, OsIAA6) in the leaf tissue were additionally assessed in two identified drought-resistant cultivars (Bala, Krasnodarskij 424) relative to a drought- sensitive common reference cultivar for rice (Nipponbare). Altogether, these data were used to investigate whether geographically diverse rice cultivars invested in reducing the effects of drought stress on the plant through distinct pathways, where differences were expected to indicate specific drought response strategies characteristic of that cultivar. Bala and Krasnodarskij 424 had diverse morphological and functional drought responses, with differences in water use, leaf developmental timing, biomass, and transcript abundance for genes OsADF3 and OsIAA6. These differences suggest that Krasnodarskij 424 may use drought avoidance strategies, while Bala may use both drought avoidance and drought escape strategies. This study aims to supplement ongoing research into the identification of agronomically beneficial drought response strategies, assisting in the targeted development of climate change-resilient crops.