Unraveling the dynamics of starch metabolism and expression profiles of starch synthesis genes in millet under drought stress

Drought impacts global food production, prompting extensive research to understand drought tolerance in millet. However, knowledge regarding the extent of tolerance achievable through acclimation remains limited. The objective of the study is to assess the effect of drought acclimation (hardening) on drought tolerance in millet and to investigate the physiological, biochemical, and transcriptional changes associated with starch metabolism in millet. To achieve this aim, two millet genotypes (‘PI 689680’ and ‘PI 662292’), exhibiting differential responses to drought stress, were subjected to various treatments: control (unstressed), drought acclimation (DA; two stress episodes with recovery), and non-acclimation (NA; a single stress episode with no recovery).. The study revealed that drought-induced oxidative stress, manifested by increased amylose, amylopectin, and total starch accumulation in NA plants compared to DA counterparts. Additionally, NA plants experienced a notable reduction in growth and photosynthetic activity. Expression patterns of starch-related transcripts were relatively elevated in NA compared to DA plants. These findings highlighted that acclimation to drought conferred tolerance to subsequent stress events by mitigating oxidative damage induced by drought stress. DA plants exhibited improved tolerance, characterized by enhanced growth, net photosynthetic rate, stomatal activity, osmotic adjustment, starch accumulation, enzyme activity, and the regulated expression of related genes. The study advocates for adopting acclimation as a strategic approach to mitigate the adverse effects of metabolic disruptions induced by drought in millet.