Regulation of Maize ( Zea mays L.) Silk Extension Tolerance to Moderate Drought Stress Associated With Sucrose Metabolism, Phytohormone and Secondary Metabolism

Drought stress prior to anthesis slows down maize silk extension and thus causes the greater anthesis and silking interval, resulting in a significant reduction in grain set. This study aims to characterise the transcriptional and physiological responses of silk elongation to moderate drought stress. A trial of two hybrids with contrasting drought tolerance, AN591 and ZD909, under well‐watered (WW) and moderate flowering drought stress (FDS) conditions was performed. Compared to the WW group, the silking under FDS was delayed by 1 day in AN591 and by 3.3 days in ZD909, suggesting that AN591 exhibits greater resilience to FDS than ZD909. The comparative transcriptomic profiling between FDS and WW for both hybrids highlighted the significance of sugar metabolism in promoting silk elongation, while also identifying phenylalanine metabolism and phytohormone signalling as inhibitory factors. Pathways exclusive to AN591 were largely linked to carbon and energy metabolism, while those in ZD909 were primarily associated with stress defence, suggesting AN591 was better adapted to FDS. Physiological assays confirmed that stronger sucrose decomposition in AN591, regulated by cell wall invertase, alleviated FDS‐induced suppression on silk elongation. This may also explain its reduced lignin synthesis and other defence responses. Conversely, the unique phytohormone signalling in ZD909, characterised by negative auxin response and positive abscisic acid response, may further exacerbate the inhibitory effect on silk elongation by driving more sugar consumption. Together, combined transcriptomic and physiological analyses revealed that the trade‐off between growth and defence was mediated through adjustments in sucrose metabolism, phytohormone signalling and secondary metabolic pathways.