Drought coupled with heat stress impairs maize silk vitality by disrupting sucrose metabolism and lignin biosynthesis

Combined heat and drought stress (HD) increases floret abortion by elevating unemerged/unfertilized emerged silk proportion. Sucrose accumulation and reactive oxygen species (ROS) overaccumulation disrupt emerged silk function under HD. HD inhibited lignin synthesis by reducing peroxidase activity. Under climate change, combined heat and drought stress (HD) during flowering increasingly threatens the maize production of the Huang-Huai-Hai region in China. While individual effects of heat (HS) or drought stress (DS) are well documented, their combined impacts—particularly on silk function—remain poorly understood. We conducted a two-year, temperature-controlled field experiment from the ten-leaf stage to silking to investigate the impacts of HD on silk function through physiological responses and transcriptomic pathways. The kernel setting rate under HD decreased significantly by an average of 56.7, 52.4, and 34.1% compared to non-stressed control, HS, and DS, respectively. This reduction was driven by increased floret abortion, resulting from unemerged silks and reduced vitality of emerged silks. Reactive oxygen species (ROS) accumulation impaired silk vitality. Transcriptomic analysis revealed that HD disrupted sucrose metabolism and lignin biosynthesis, leading to reduced glucose, fructose and lignin content. Peroxidase activity declined by 32.5, 38.7, and 46.1% under HS, DS, and HD conditions, respectively, while lignin content decreased by 24.4, 34.4, and 44.3%. Phenylalanine ammonia-lyase and cinnamyl alcohol dehydrogenase activities increased under stress, with the strongest upregulation observed under HD. HD synergistically suppressed the vitality of emerged silks by promoting sucrose and ROS accumulation while reducing lignin content, leading to increased floret abortion and kernel loss. These findings highlight a synergistic interaction between drought and heat stress in maize.