Physiological Response And Transcriptomic Analysis In Response To Drought Stress In Foxtail Millet(Setaria Italica L.)

Drought is one major abiotic stress factor affecting crop production.Foxtail millet,as a model crop in drought resistance research,is of great significance for studying the drought resistance molecular mechanisms of crops and guiding agricultural production.To uncover the drought-resistant candidate genes of foxtail millet and identify the molecular regulatory mechanisms and metabolic pathways of drought resistance,here we selected 44 samples of foxtail millet materials for identification and screening of drought-resistant germplasm resources.After screening,the highly drought-resistant variety M79,its maternal E1 and paternal H1 were included in the transcriptome sequencing.The differentially expressed genes(DEGs)of the three samples under drought stress were analyzed,and the functional enrichment and pathways of the DEGs were investigated,aiming to identify the drought resistance molecular mechanism of foxtail millet.(1)The drought resistance indicators of 44 samples of foxtail millet materials were evaluated and screened,and drought stress was simulated using 20%PEG-6000.The relative root lengths,bud lengths,survival rates,root length inhibition rates,and bud length inhibition rates were all compared to evaluate the drought resistance of all 44 samples at the germinating phase.It was found M79 showed very strong response to drought stress and high drought resistance.(2)The hybrid F1 M79 with high drought resistance,its maternal E1 and paternal H1 were selected,and the differences of physiological phenotypes under drought stress were investigated using the seedling-stage natural drying method.It was found under drought stress,the activities of antioxidant enzymes(catalase,peroxidase)of M79 were significantly higher,the declining amplitude of its leaf water potential(LWP)was lower,and its photosynthetic energy conversion efficiency was higher compared with its parents.On the 6th day of drought stress(soil water content was～20%),leaves were collected for transcriptome sequencing.The RNA-seq uncovered 3066,1895 and 2148 DEGs in M79,E1 and H1,respectively,with 288 DEGs shared among the three.Six genes were validated by qRT-PCR,and the results were very significantly and positively correlated with the RNA-seq expression levels.Gene ontology(GO)enrichment and Kyoto Encyclopedia of Genes and Genomes(KEGG)analysis showed M79,E1 and H1 significantly enriched 17,11 and 19 GO terms,respectively and 14,6 and 9 KEGG pathways,respectively.Then these results were comparatively analyzed to identify the significantly differential enrichment pathways among the three samples.The GO terms and KEGG pathways significantly enriched by M79 included the post-translational modification,photosystem II oxygen-evolving complex,peroxidase activity,protein kinase activity,phytohormone signal conduction,and chlorophyll biosynthesis pathways.Co-regulation analysis showed the DEGs of M79 after drought stress formed a regulatory network involving multiple biological processes and pathways,including photosynthesis,signal transduction,transcriptional regulation,redox regulation,hormonal signaling and osmotic regulation.(3)RNA-seq analysis also showed that under drought treatment,some photosynthesis-related DEGs were highly expressed in M79 compared to its parents.On this basis,the photosynthesis regulatory pathway of M79 under drought stress was further analyzed.It was found 10 key genes were involved in regulating the photosynthesis pathway of M79 under drought treatment,which was deduced to be the reason why M79 maintained high photosynthesis under drought stress.This study revealed the drought resistance molecular regulation pathway of M79,especially the photosynthesis pathway regulation under drought stress.The drought resistance molecular mechanism of foxtail millet was addressed,which provided abundant molecular information and a theoretical basis for further analysis of the underlying mechanism.