Mechanism Of Melatonin Regulating Maize Pollen Response To High Temperature Stress

With the occurrence of extreme heat around the world,more and more summer crops are exposed to the harm caused by high temperatures.As the main food crop in summer,corn’s tasseling stage is a sensitive period affected by high temperature.High temperature can reduce the pollen amount,activity,and nutrient imbalance of corn tassels.Applying chemical regulators to improve the crops’ high temperature tolerance is a simple and efficient technical approach,Melatonin,MT plays an important role in the life processes of plants and animals,and can significantly improve the ability of plants to withstand adversity.In this study,Zhengdan 958(ZD985,heat-insensitive type)and Xianyu 335(XY335,heat-sensitive type),two maize varieties with different temperature sensitivity,were used.During the leaf spreading period of Maize 10,the whole plant was sprayed with MT with a concentration of 100 μmol/L,and the whole plant was heated by plastic greenhouse.From 8:00 to 18 every day: To explore the regulatory effect of MT on maize pollen under high temperature stress.The results show that:MT could significantly alleviate the damage to the tassels of the two maize varieties under high temperature stress,especially the high temperature sensitive variety Xianyu 335.By increasing the length,size,volume and weight of the tassels,MT could increase the effective pollination time and loose powder amount.Improve the morphological structure of anthers and pollen damaged by high temperature,enhance the pollen vitality,and then increase the seed setting rate and maintain the yield of maize.In addition,MT spray can effectively improve the activity of antioxidant enzymes in corn male ears,thus effectively alleviating excessive accumulation of peroxides and other harmful substances caused by high temperature.In addition,MT spray can also increase the content of osmotic regulatory substances(soluble sugar and soluble protein)in corn male ears under high temperature,and increase pollen stress resistance.Transcripome analysis of Xianyu 335 maize pollen showed that high temperature stress could significantly increase the differentially expressed genes(DEGs)in the amino acid-related degradation and anabolic pathways,accelerate the metabolic activities of amino acids,fatty acids and other nutritional molecules,reduce the content of soluble protein,and increase the content of anti-stress factor proline.Application of MT can stimulate the up-regulated expression of novel.703,effectively stimulate gibberellin(GA)related metabolic pathways and increase GA content.Metabolomic analysis of Xianyu 335 maize pollen showed that the expression of metabolites flavonoids was down-regulated under high temperature stress,and the related metabolic pathways of sugars in the differential metabolite(DMs)enrichment pathway tended to be down-regulated.However,after spraying MT,the expression of flavonoid differential metabolites and related metabolic pathways of carbohydrate was up-regulated,which increased the contents of flavonoid and carbohydrate metabolites,helped to maintain the stability of the osmotic regulation system of pollen cells,and improved the stress tolerance of maize pollen cells.Transcriptome and metabolome analysis of Xianyu 335 maize pollen showed that novel.703 gene of plant hormone signal transduction pathway was up-regulated by exogenous MT under high temperature stress,and GA content was increased.The expression levels of jasmonic acid(JA)and Jasmonyl-L-isoleucine(JA-ILE)in α-linolenic acid metabolism pathway were down-regulated.Therefore,the coordination of complex plant hormone signaling networks and synthetic pathways to alleviate high temperature stress plays an important role in improving the heat tolerance of maize male ear.The results of this study provided a new direction and theoretical basis for the future research on improving crop resistance to high temperature by using MT.