Analysis Of Root Physiology And Membrane Lipid Metabolism Of Mize Sedlings Under Low Temperature Stress

Maize(Zea mays.L)is the main food crop in China.Northeast China is the main corn producing area in China.Low temperature is one of the main abiotic stresses that restrict the growth of maize seedling in northern China.Our research group found in previous research that the leaves of maize seedling under low temperature stress had obvious responses at physiological,biochemical and molecular levels,combined analysis of transcriptome and lipidome shows significant activation of membrane lipid metabolism and lipid signaling pathways at low temperatures.In this study,the maize inbred line He-344 was used as the experimental material,and the 2-week old maize seedlings were treated at a low temperature of 5?.The physiological changes,membrane lipid metabolism and gene expression patterns of maize seedling roots under low temperature stress were studied,to further understand the tolerance of maize to low temperature and provide theoretical basis for creating low temperature resistant maize varieties.1.In this study,transcriptome sequencing was performed on maize seedling roots treated with low temperature(5?)and control(22?)for 3 days.The results show that 8482 differentially expressed genes(|log2FC|?1)were screened in the control group,among them,4562 up-regulated differentially expressed genes,and 3920 down regulated differentially expressed genes were found.By functional annotation of differentially expressed genes,it was found that most genes were annotated to metabolic pathway.It was also found that transcription factors were involved in the cold response of maize,such as MYB,WRKY,b HLH and NAC;In WRKY family,AC209050.3_FG003 and GRMZM2G516301 expression folds were more than 8,in MYB family;GRMZM2G176327 gene expression folds were 7.7.2.Under low temperature stress,the activities of superoxide dismutase(SOD),peroxidase(POD),and the content of proline(Pro)and malondialdehyde(MDA)in maize seedling roots increased with the extension of treatment time.At the same time,10 Zm SOD genes were screened from the transcriptome data,and 8 Zm SOD genes were up-regulated.Twelve up-regulated Zm POD genes were screened,among which Zm POD35,92,94 and 108 were significantly up-regulated.Ten genes encoding lipoxygenase(LOX)were screened,which were closely related to malondialdehyde content,among them,Zm LOX4,7,8 and 9 genes were significantly up-regulated.3.Lipomics analysis was performed on maize seedling roots under low temperature stress,and a total of 12 lipids were detected.The content of PC in maize seedling roots is the most abundant.Under low temperature stress,the percentage of PC,PI,PE and PA in phospholipids increased,and the percentage of PA increased by 63.2% compared with the control,the percentage content of PG and PS decreased;the content of DGDG increased,the content of MDGD decreased,and the content of SQDG did not change significantly.In lysophosphatidylcholine,the percentage of LPG increased by 128.8% compared with the control;there was not significant change in the percentage of LPC and LPE.Screening of lipid-regulating genes in the transcriptome data,a total of 189 differential genes were screened,and they were annotated into 14 lipid metabolic pathways,among them,106 genes were up-regulated and 82 genes were down-regulated.“Phospholipid Signaling”“Fatty Acid Elongation & Wax Biosynthesis” and “Eukaryotic Phospholipid Synthesis & Editing”are the most abundant differentially expressed genes,indicating that phospholipid metabolism may be activated under low temperature stress.4.A total of 30 fatty acid desaturases were identified from maize genome,including 13 soluble and 17 membrane-bound fatty acid desaturases,which were further classified into 2 and5 sub-groups,respectively,via phylogenetic analysis.Although there is no evolutionary relationship between the soluble and membrane-bound fatty acid desaturases,they all harbor a highly conserved FA_desaturase domain,and the types and distributions of conserved motifs are similar within each sub-group.Expression analysis of fatty acid desaturase genes in maize leaves under low temperature stress by q RT-PCR;the expression of Zm FAD2.1&2.2,Zm FAD7 and Zm SLD1&3 were significantly up-regulated under cold stress.The co-expression analysis demonstrated close correlation among the transcription factors and the significant responsive fatty acid desaturase genes under cold stress.This study will help to understand the roles of plant fatty acid desaturases in temperature stress responses.