Transcriptomic And Metabolomic Analyses Of Defense Responses Of Upland Cotton To Verticillium Dahliae

Verticillium wilt is caused by Verticillium dahliae infection and is one of the most destructive biological factors limiting cotton production.Mechanistic details of cotton defense responses to Verticillium wilt remain unclear.In this study,the defense response of cotton to V.dahliae was revealed by the combined analysis of transcriptome and metabolome.V.dahliae is a kind of soil-borne disease fungus.Green fluorescent protein(GFP)is a protein that can emit fluorescence.In this study,GFP-labeled strain V592-GFP of V.dahliae was used to track colonization in cotton roots.No green fluorescence was observed at 0 and 12 hours post-inoculation(hpi)of cotton roots with V592-GFP,At 24 hpi,weak fluorescence signals were observed,while at 48 hpi,strong fluorescence signals were observed in cotton roots.At 96 hpi,numerous hyphae appeared and populated the root cells.At 28 days post-inoculation(dpi),green fluorescence was found to fill the field of view.The results showed that 48 hpi timepoint is the critical period for V.dahliae penetration into cotton.When the pathogen invades the plant,the plant will undergo a series of reactions to resist the invasion of the pathogen.Transcriptome and metabolome can reveal the interaction between plants and pathogens at the overall level.At present,there is a lack of research in this field in cotton.In this study,transcriptome analysis found that 1523 differentially expressed genes(DEGs)were identified in the cotton roots at 24 hpi,and 8270 DEGs were identified in the cotton roots at 48 hpi.Metabolomic analysis found 78 differentially accumulated metabolites(DAMs)at 48 hpi.Conjoint analysis indicated that phenylpropanoid biosynthesis,tryptophan metabolism,flavonoid biosynthesis,isoflavone biosynthesis and other pathways were significantly enriched.Analysis of important pathways revealed that 42 DEGs and 5 DAMs were involved in phenylpropane biosynthesis,and 14 DEGs and 3 DAMs were involved in flavonoid biosynthesis.Plants can synthesize metabolites to inhibit the growth of pathogenic bacteria or kill pathogenic bacteria to resist the invasion of pathogenic bacteria.This study used the up-regulated DAMs related to phenylpropanoid biosynthesis and flavonoid biosynthesis to conduct antibacterial experiments in vitro.For the DAMs ofphenylpropanoid biosynthesis,caffeic acid,coniferyl alcohol,coniferin,scopoletin and scopolin could inhibit the growth of V.dahliae,but for the DAMs of flavonoid biosynthesis,naringenin,dihydrokaempferol and eriodictyol were not effective,they were lower than the DAMs of phenylpropanoid biosynthesis.In conclusion,this study confirmed that 48 hpi timepoint is the critical period for V.dahliae penetration into cotton through the GFP-labeled observation experiment of colonization.Through conjoint analysis of transcriptome and metabolomic revealed that phenylpropanoid biosynthesis,tryptophan metabolism,flavonoid biosynthesis and isoflavone biosynthesis changed during the infection of V.dahliae.Through in vitro antibacterial experiments on metabolites related to the biosynthesis of phenylpropanoid and flavonoids,it was clarified that phenylpropanoid biosynthesis is a key pathway for cotton to resist the invasion of V.dahliae.These results have increased the understanding of cotton’s defense response to V.dahliae and contribute to the prevention and control of cotton Verticillium wilt.