Analysis Of New Maize Variety Zhengdan309 Heat Stress Response Mechanism Based On Transcriptomics And Metabolomics

Maize is one of the most important food crops in the world,high temperature is the main meteorological disaster in Huanghuaihai summer maize production,its damage to maize at the seedling stage has always been a concern in maize production.Zhengdan309 is an excellent new maize variety bred by our research group,the heat tolerant variety identification test shows that it has excellent heat tolerance characteristics.In this paper,by studying the physiological indexes,transcriptome profile and metabolome profile of Zhengdan309 and its parents（male parent:Zheng M189;female parent:Zheng H39-1）after 3 days and 6 days of heat stress at the seedling stage,the response mechanism of maize heat stress was analyzed.The main results are as follows:1.With the prolonged stress time,the content of MDA and H₂O₂in Zhengdan309 and its parents all showed an upward trend,among them,Zhengdan309had the smallest increase and the lowest content;the content of proline and soluble protein all increased first and then decreased;the content of soluble sugar continued to increased;the content of chlorophyll continued to decreased;the contents of these4 physiological indexes were all the highest in Zhengdan309;the activities of SOD,POD,and CAT were all firstly increased and then decreased,among them,Zhengdan309 has the highest enzyme activity,Zheng H39-1 takes the second place,and Zheng M189 has the lowest enzyme activity.The results show that Zhengdan309has good heterosis relative to its parents,and it is expected to improve the heat tolerance of maize through cross breeding.2.At two time points of heat stress,299 core heat-responsive genes were found in Zhengdan309 and its parents,mainly encoding protein kinase superfamily proteins,peroxidases and heat shock proteins（Hsp90,Hsp101,s Hsp）,etc.Among them,the gene encoding Hsp101 was significantly up-regulated,with the smallest up-regulation in Zheng M189 and the largest up-regulation in Zhengdan309,heat stress for 3 days and 6 days increased by 221.9 times and 65.2 times in Zhengdan309,respectively.Pathway enrichment analysis found that,Zhengdan309 and its parents have both conservative pathways and unique pathways to cope with heat stress.Conservative pathways including Response to heat,Oxidoreductase activity,and Sugar transmembrane transporter activity.However,the up-regulated DEGs in Zhengdan309 were significantly enriched in pathways related to stress response（such as Response to water deprivation,Response to hydrogen peroxide,and Response to reactive oxygen species）.3.150 common heat-responsive metabolites were identified in Zhengdan309 and its parents.Under heat stress,metabolites such as mannose-6-phosphate,flavonoids,coumarin,zeatin and jasmonic acid were all highly accumulated in Zhengdan309 and its parents;Among them,the accumulation of jasmonic acid is the most significant,under heat stress,the jasmonic acid content in Zhengdan309 is the highlyest and the increase is the largest,and the content in Zheng M189 is the lowest and the increase is the smallest.4.The combined analysis of transcriptomic and metabolomic found that the changes of DEGs and downstream DEMs in Fructose and mannose metabolism,Cysteine and methionine metabolism,andα-Linolenic acid metabolism pathways were basically the same,these pathways play a crucial role for heat resistance in maize.The activity of POD increased after heat stress,and it was found that the change trend of the expression of the gene encoding POD was consistent with the physiological results,indicating the antioxidant enzymes in maize participate in the heat response and remove reactive oxygen to alleviate the damage caused by heat;The soluble sugar content in maize seedlings increases with the prolonged heat stress time,and a large accumulation of soluble sugarsα-D-glucose and trehalose in the metabolic profile was also found,and also found the genes up-regulated in Zhengdan309 and its parents were significantly enriched in sugar metabolism pathways such as Sugar transmembrane transporter activity,Amino sugar and nucleoside sugar metabolism,and Starch and sucrose metabolism;While mannose-6-phosphate accumulates significantly,it can alleviate heat stress by promoting glycolytic pathway.By comparing the heat-respositive genes and metabolites of Zhengdan309 and its parents,found that the overlapped genes/metabolites between the two parents were the least,and the overlap between the hybrid and the female parent was the most,combined with physiological indicators,indicating the female parent has a greater genetic contribution to the heat resistance of the hybrid,and the hybrids was more resistant to heat stress.In summary,it is speculated that maize response to heat stress by sugar metabolism pathway,jasmonic acid（JA）regulation and reactive oxygen scavenging system;the genes,metabolites and key pathways excavated in this paper provide a theoretical basis for the study of maize heat stress response mechanisms.