Leaf Function And Transcriptome Study Of Cotton Virescent Mutant

The first true leaf of cotton virescent mutant showed bud yellow phenomenon at the seedling stage.The virescent mutation can be used as an indicator trait during breeding,which greatly saves labor costs and causes widespread concern of breeders.Leaves are the site of photosynthesis in plants,and leaf color mutants are ideal materials for studying plant photosynthesis.In this study,the wild type plants of cotton were used as control.The changes of chlorophyll content and photosynthesis of cotton virescent mutants in different growth stages,the physiological mechanism of cotton virescent mutation and the effect of virescent mutation on photosynthesis of cotton plants were studied.The cotton virescent mutant at the seedling stage and the first true leaf of the wild type were sequenced by transcriptome,and the mutation mechanism of the cotton virescent mutant was analyzed from the gene expression level.The main results were as follows:1、The measurement of pigment content of leaves at different growth stage showed that the content of chlorophyll a,chlorophyll b and carotenoid in the new leaves of cotton virescent mutant plants were significantly lower than that of the control leaves,only 49%,31%,45%of the control cotton.But with leaf growth,the chlorophyll and carotenoid content of the leaves of the virescent mutant gradually increased and reach the level of control leaves.The full-wavelength scan of the 80%acetone pigment extraction showed that there was no significant difference in pigment composition between the virescent mutant and the control leaf,but there was a difference in pigment content.The ultrastructural research of chloroplast showed that the number of chloroplasts in the leaves of virescent mutants was small and there were some defects in chloroplast development,and the number of thylakoid membranes was little.In contrast,the chloroplasts of the control leaves were completely developed,and the thylakoids were perfected.The total protein extraction results of virescent mutant yellow leaves,yellow-green transforming leaves,green leaves and control leaves showed there was no significant difference in protein types between virescent mutant leaves and control leaves.The stomatal distribution and opening degree of the virescent mutant and the control leaf showed that the stomatal opening degree of the virescent mutant was higher than that of the control leaf.2、The results of chlorophyll fluorescence parameters at different growth stage and seedling photosynthesis in leaves of virescent mutants and control leaves showed that the Pn of cotton virescent mutant leaves was higher than that of control leaves,which may be related to the stomatal factor,light absorption capacity and PSII photochemical efficiency of cotton virescent mutant leaves were higher than those of the control leaves;the ability of cotton virescent mutants leaves to dissipate excess light energy as heat is higher than the control leaves may be related to stomatal and higher transpiration rate;the diurnal variation of photosynthesis of the virescent mutant and control showed that the diurnal variation of net photosynthetic rate,stomatal conductance and transpiration rate of the virescent mutant leaves was similar,and the net photosynthetic rate,stomatal conductance and transpiration of the virescent mutant was higher than control;the diurnal variation of intercellular CO2 concentration was different from the other three parameters,the intercellular CO2 concentration of the virescent mutant was lower than control;the results of light response curves of virescent and control showed that the response of virescent mutant to light was higher than that of control,and the light saturation point and light compensation point of bud yellow mutant were lower than control,the saturated photosynthetic rate and apparent quantum efficiency of virescent mutant were higher than control,the stomatal conductance of cotton virescent mutant and control increased with the increase of light intensity,and in the range of 0-2000μmolm-2s-1,the stomatal conductance of virescent mutation was higher than control;the PI(abs),10RC/ABS and Kn of the virescent mutant were higher than that of the control at different growth stages,Fv/Fm and Fv/Fo of the virescent mutant were higher than the control.3、A total of 65,126 Unigene were detected in the transcriptome sequencing results of the first ture leaf from the cotton virescent mutant and control plant,of which 59,775 Unigene were known.6768 differentially expressed genes(DEGs)were obtained in virescenr mutant,in which 4002 DEGs were up-regulated and 2766 DEGs were down-regulated.A total of 4891 DEGs were mapped to 2450 GO terms in the GO database,of which 1331 GO terms were enriched into the biological process category,318 GO terms were enriched into the cellular component category,and 801 GO terms were rich into the molecular function category,they accounted for 54.3%,13.0%and 32.7%.KEGG analysis mapped 2784 DEGs to 134 KEGG pathways,and 926 DEGs were mainly involved in plant-pathogen interaction,MAPK signaling pathway-plant and Plant hormone signal transduction.In the porphyrin and chlorophyll metabolic pathway,the genes encoding glutamate-1-semialdehyde 2,1 aminomutase,Mg-dechelatase and chlorophyll a oxygenase were different expressed in cotton virecsent mutant leaf,this gene may related to virescent mutant.In the photosynthesis pathway,PsbC、PsbB、PsaA and PsaB were down-regulated expression in the cotton virescent mutant,the light harvest and electron transfer of photosynthesis in the virescent mutant were influenced;PsbS was up-regulated expression in cotton virescent mutant,indicated that the ability of the virescent mutant to dissipate excess light energy into heat was enhanced.