Analysis Of Photosynthetic Physiological Characteristics And Related Gene Expression Partterns Of Yellow Leaf Mutant In Betula Platyphylla

Leaf color mutants are important materials for studying plant photosynthetic physiological characteristics,chlorophyll synthesis,chloroplast development and related gene expression.Our previous study found a yellow leaf mutant lines among the overexpression lines of Cinnamoyl-coA Reductase 1(BpCCR1)gene in birch,it was named yl lines(yellow leaf).The BpCCR1 gene is key enzyme in the biosynthesis pathway of lignin,and it is of great significance for the biosynthesis of lignin.Since the leaf color of other overexpressing lines is normal,no studies have shown that the BpCCR1 gene has this function,it was concluded that the variation of the yl lines was caused by the function of the leaf color related genes.In this study,wild birch WT,35S::BpCCR1 transgenic OE11 and yl lines were used as materials,and the leaf color parameters,photosynthetic pigment content,photosynthetic parameters,gene expression and salt tolerance of the tested lines were analyzed.At the same time,LncRNA(Long non-coding RNA)and miRNA(microRNA)were sequenced in the tested lines to analyze the differentially expressing LncRNA and miRNA and the functions of their target genes.The research results are as follows:(1)The relative chlorophyll content of yl lines in the whole growth period was significantly lower than that of the two control lines.The leaf color parameters L*and b*were significantly higher than the two control lines,while the leaf color parameter a*were significantly lower than two control lines.The chlorophyll a,chlorophyll b,total chlorophyll content and carotenoid content of the tested lines gradually increased from the second leaf to the tenth leaf.The chlorophyll a,chlorophyll b,total chlorophyll content and carotenoid content of the yl lines were significantly lower than the two control lines,the chlorophyll a,chlorophyll b,total chlorophyll content and carotenoid content of the fourth leaf of yl lines were about 41.71%,28.87%,30.11%and 30.81%,respectively,of the average of the two control lines.(2)The net photosynthetic rate(Pn),stomatal conductance(Gs)and transpiration rate(Tr)of the third to the tenth leaf of the tested lines showed a decreasing trend.The yl lines Pn,Gs and Tr were lower than the two control lines.The Pn,Gs and Tr of the fourth leaf of yl lines were only 61%,31%and 37.5%of the average of the two control lines.(3)The BpGLKl gene associated with chloroplast development was hardly expressed in yl,and the expression patterns of genes related to chlorophyll synthesis are basically consistent among the tested lines.The relative expression levels of BpLhca3,BpLhcbl,BpLhcb2 and BpLhcb4 genes related to photosynthesis in yl lines were lower than those of two control lines.(4)The relative seedling height growth of the tested lines under long-light treatment was significantly higher than that of short-light treatment,while the relative seedling height growth of yl lines was significantly higher than that of the two control lines at 30 days of short-light treatment.The contents of ChIa,ChIb,ChI and Car of the same lines under long-light treatment were significantly higher than that under short-light treatment.The maximum photochemical efficiency(Fv/Fm)of tested lines under long-light treatment was significantly higher than that of short-light treatment.The Pn of the two control lines under long-light treatment was significantly higher than that of short-light treatment,while Pn of yl lines under long-light and short-light treatments was not significantly different.(5)Different light intensity treatments showed that the relative seedling height growth of tested lines under normal light conditions was significantly higher than that of strong light and weak light conditions,while the relative seedling height growth of yl lines under high light conditions was significantly higher than the two control lines.The contents of ChI,ChIa,ChIb and Car of yl lines under strong light conditions were significantly higher than those under normal light and weak light conditions,which were 139.02%,151.65%,110.92%and 153.2%of yl lines under normal light conditions,were 156.02%,170.66%,123.72%and 156.28%of yl lines under weak light conditions.(6)The salt treatment results of tested lines indicated that the two control lines have strong salt tolerance and the yl lines has weak salt tolerance.(7)A total of 2187 LncRNA were obtained by LncRNA sequencing.53 LncRNA are differentially expressed in WT_vs_yl and OE11_vs_yl,and their target genes are involved in 38 metabolic pathways,including biosynthesis of secondary metabolites,purine metabolism,citrate cycle,pentose and glucuronate interconversions.A total of 274 miRNA were obtained from miRNA sequencing.The level of miRNA expression indicated a significant change in the yl lines compared to the two control lines.32 miRNA are differentially expressed in WT_vs_yl and OE11_vs_yl,and their target genes are involved in 16 metabolic pathways,including protein processing in endoplasmic reticulum,zeatin biosynthesis,sulfur metabolism,protein export and galactose metabolism.In summary,the photosynthetic pigment content and net photosynthetic rate of yl lines were significantly decreased.Treatment with different light conditions showed that the light response of the yl lines was different from that of the two control lines.In this study,the yl lines was studied from the perspective of photosynthetic physiological characteristics and related gene expression patterns.It not only enriches the basic research of woody plants on leaf color mutants,but also provides some reference for the study of other leaf color mutants.