Heat-resistant Screening And Transcriptome Sequencing Analysis Of Maize Inbred Lines

Maize(Zea Mays L)is one of the main crops in China.The global warming brings a serious threaten to corn yield in recent years.In order to cope with the threat of heat stress on corn production,it’s urgency to identify excellent thermotolerant maize germplasm resources and cultivate thermotolerant new maize varieties.This experiment aims to establish rapid and accurate methods for screening new heat-tolerant maize germplasm,and initially identified heat-resistant and heat sensitive maize inbred lines by three different methods.Furthermore,RNA-sequencing analysis was carried out to decipher transcriptional regulation mechanism underlying surveyed sensitive and heat tolerant inbred lines under heat stress.The main results are as follows:(1)Thermotolerant germplasms were screened by three methods.We grew seedlings in soil and culture solutions,respectively,and assess their heat resistance under 45℃.Additionally,we germinated surveyed maize varieties on sand and assess their thermotolerance under 50℃ at the germination stage.Compared with the methods of hydroculture and soil culture at seedling stage to assess thermotolerance,sand culture at the germination stage apparently shorten the time,and saves space and materials.(2)Heat-tolerant inbred line HY153 was screened from our four surveyed maize inbred.We also identified that the sequenced maize inbred line B73 is a heat sensitive maize.In addition,we also screened the Insertion mutation A5 is a heat-sensitive phenotype.And the W22 is genetic background of A5.(3)Maize seedings(B73 and HY153)at the three-leaf stage were exposed to heat shock at 45℃ for 6 h.After heat shock treatment,severe symptoms of leaf wilt and yellowing were observed in B73 inbred lines,whereas HY153 exhibited normal phenotypes.The results of physiological indexes and photosynthesis indicators under high temperature stress indicated that high temperature seriously damaged the photosynthetic system of B73,while HY153 would maintain normal function.The content of hydrogen peroxide and malondialdehyde in B73 was higher than HY153.The results of the content of proline revealed that the tolerance inbred line HY153 was significantly higher than B73.(4)In order to further clarify the heat shock responses,the leaves of B73 and HY153 exposing to heat shock were collected and sequenced.After exposing to 45℃ for 6 h,a total of 1976 and 4649 genes were differentially expressed in B73 and HY153,respectively.However,after recovery from heat stress for 1 h at 28℃,the numbers of differentially expressed genes were reduced to 243 and 2335 in B73 and HY153,respectively.Moreover,GO and KEGG analysis showed that these differentially expressed genes were enriched into the endoplasmic reticulum membrane protein process,which may contribute to heat stress responses.In conclusion,our finding indicated that maize protect themselves against heat stress by reducing growth and enhancing photorespiration and improve heat tolerance by activating calcium ion pathway and inducing DnaJ-like protein family.Interestingly,three heat shock transcription factors specific to HY153 were highly enriched and selected for further study,which provide important genetic resources for further study.