Analysis Of Photosynthetic Characteristics And Differentially Expressed Genes Of A Tomato Yellow Leaf Mutant LA3734

Leaf color mutants are ideal materials for studying a series of fertility processes such as photosynthesis,hormone physiology,material and energy metabolism.As one of the widely cultivated cash crops and model crops,yellow-leaf mutants of tomato(Solanum lycopersicum)have long existed,however,the mechanism of its variation has not been clarified yet.In this study,the yellow-leaf mutant LA3734,which is newly screened from the tomato EMS mutant library,and its wild-type AC strain are used as test materials.The tomato yellow-leaf mutant plant growth and photosynthetic physiological changes are analyzed and the related differentially expressed genes are screened,which are expected to lay the foundation for the discovery of functional genes controlling tomato leaf color and the in-depth analysis of the mechanism of leaf color variation.The main research results are as follows:1.It is clarified that the yellow-leaf mutant plant LA3734's yellow leaf phenotype,slow and weak growth situation continue throughout the growth period,and its plant height and stem thickness are significantly lower than those of the wild type in the same period,especially the dwarfing trait,indicating that its growth is significantly inhibited.At the same time,it is clarified that the number of chloroplasts is significantly reduced,the structure is seriously damaged,and the development is obviously poor in mesophyll cells of the yellow-leaf mutant LA3734;and the contents of chlorophyll a and total chlorophyll,chlorophyll synthesis precursors PBG,Urogen?,Coprogen?,Proto?,Mg-Proto? and Pchlide in leaves are obviously lower than those of wild type,in which Urogen ? content decreases most severely.It is speculated that the yellowing of tomato leaves is mainly due to the significant reduction in chlorophyll a content which results from the destruction of the chlorophyll synthesis site,and the whole seriously inhibited synthesis process,especially the obstruction of Urogen ? synthesis.2.The analysis confirms that the leaf photosynthetic gas exchange parameters Pn,Tr,and Gs of yellow-leaf mutant LA3734 are significantly lower than wild type,while Ci has the opposite trend,indicating its photosynthetic capacity is significantly weakened.And its Chlorophyll fluorescence kinetic parameters Fv/Fm,Y(II),q P,NPQ,Y(NPQ),and ETR(II)are significantly lower than those of the wild type,while Y(NO)is significantly increased,indicating that PSII activity is reduced and its function is severely damaged.Although its Pm is remarkably lower than the wild type,there is no obvious difference between Pm',Y(I),ETR(I)and those of the wild type,and Y(ND)is higher while Y(NA)is lower,indicating that the selfregulation capacity of ETR(I)is stronger so that the activity of PSI is less affected.The results suggest that the decrease of photosynthetic rate of leaves resulting from its yellowing phenotype is mainly caused by the decrease of PSII activity and the severe damage of its function.3.Transcriptome sequencing of plant leaves of tomato yellow-leaf mutant LA3734 and wild-type AC is performed,and the quality of the data obtained is well evaluated.Analysis shows that there are 2681 significantly differentially expressed genes,of which 1079 are upregulated and 1602 are down-regulated.Among them,the analysis of the porphyrin and chlorophyll metabolism pathways reveals that in the entire pathway from the starting point of chlorophyll synthesis,L-glutamyl-t RNA,to the synthesis of chlorophyll a and chlorophyll b,the differentially expressed genes encoding related enzymes except for one gene related to heme synthesis are all down-regulated,and the differentially expressed genes related to photosynthesis are concentrated in PSII and PSI,all of which are down-regulated.In addition,the synthesis of chlorophyll in the metabolism of terpenoids and the synthesis and signal transduction pathways of plant endogenous hormones cytokinin and brassinosteroids,which are closely related to plant photosynthesis,are inhibited to some extent,while the expression of abscisic acid signal transduction genes is promoted.The transcriptome sequencing results further illustrate that the yellow color variation of mutant LA3734 may be closely related to the decline of the overall chlorophyll synthesis ability because of the inhibition of multiple enzymatic reactions during the chlorophyll synthesis process,the poor development of chloroplasts,the decrease in the protein content and the structural damage of the light-capturing protein complex.It is thought that the above plant hormone levels will also have a certain effect on plant leaf color.4.Differentially expressed genes screened by transcriptome sequencing analysis are also enriched in carbohydrate metabolism-related pathways such as starch and sucrose,lipid metabolism-related pathways such as steroids,keratin and xanthomone and wax biosynthesis,amino acid metabolism-related pathways such as the glutamine family,biosynthesis and metabolic pathways of secondary metabolites such as terpenoids and flavonoids,cofactors and vitamin metabolism-related pathways,and DNA replication and repair-related pathways and so on.Further analysis reveals that most of the genes involved in carbohydrate,lipid,and protein metabolism,including coenzymes involved in the reaction of the yellow-leaf mutant LA3734 are down-regulated,indicating that the main metabolic pathways of tomato leaves are inhibited to varying degrees after yellowing.These may become one of the important reasons for further explaining the phenotype of tomato yellow-leaf mutant LA3734,which is short and weak in growth potential to some extent.