| Pepper is an important vegetable crop,andit is of great significance to develop germplasm of Capsicum with different leaf colors for the production of a generation of hybrids,varieties of Capsicum for leaves and ornamental Capsicum,and improve insect resistance of Capsicum.However,so far,pepper leaf-color generesourceshave beenlacked,and the genetic mechanisms of leaf color are not very clear.Therefore,by obtained pepper light-green leaf mutants by mutagenesis,and combined with other pepper leaf color mutants obtained previously by the project group,this article analyzed the development characteristics and genetic mechanism of leaf color mutants,and explored the regulation effect of key leaf-color genes on pepper leaf color.The main findings are as follows:1.Screening and identifying pale green-leafedpepper mutantzylm by mutagenesis meansEthylmethane sulfonate（EMS）was used to mutagenize seedsof pepper cultivar“Zunla”and the first mutant generation（M1）ant M2generationwere investigated and analyze.It is found that various mutationswere observed in the M1generation and part mutationswere inherited to offspring.By screening and identification ofthe M2 individuals,we found that leaf-color,leaf-shape,and dwarfism.Therein,No.418-7 individual from the generation showed the characteristics of leaf-color mutation and retardedgrowth,and no charactersegregation was observed in its offspring.The mutant wasnamed as zylm.2.Chlorophyll deficiency resulted in poor pepperdevelopment,butanthocyanin accumulation improved the growth of pepper.By observation morphologicallyand measurementof physiological and biochemical parameters of zylmand other leaf-color pepper mutants（purple leaf mutant z1 and yellow green leaf mutant bmy）obtained previously by the project group,we found thatcompared with the control（green leaf pepper cultivars Zunla and B12）,themutantszylmshowed retarded growth with dwarfism and pale green leaves,and poor developed roots,low leaf-pigment contents were,weak photosynthesis.Mutant bymshowed yellow-greenleaf-color,and had lower chlorophyll content,worse photosynthesis capacity thanzylm,but its root activity was similar to zylm.Leaves of the mutantz1were thick and wide with dark purple colorand root wasstrong.Also,its anthocyanin content androot activity were high,but the photosynthesis was weak.Furthermore,carotenoids proportion in the leaves of these mutants were little,and a little significant difference in the expression of carotene-related genes was observed.There was significant difference in the chlorophyll and anthocyanin contents as soon asthe expression of the two pigmentssynthesis-related genes,indicating that the leaf-color mutation of pepper is closely related to the metabolism of chlorophyll and anthocyanin,and presentation of leaf-colorwas determined bythe three pigment contents.3.The inheritance of both pale greenand purple leavesis controlled by the nucleus,and the CaPAL gene plays an important role in formation of purple leaves.In the 543 F2individuals constructed by zylm and Zunla,140 plants showed segregation of leaf color,and be fit to the Mendelian separation law,indicating thatinheritanceof pale green in mutant zylmbelonged to the single gene recessive inheritance model.The pal green leaf gene ZYLM was mapped to rSSR003 and rSSR09-3 on chromosome 3 by gene location technology,and the objective region contains 39 genes,but no genes related to chlorophyll synthesis were observed.In the F2 generation of 273 individuals constructed by purple leaf mutant z1 and green leaf cultivar P126,200 individuals showedsegregation of purple-green leaf-color.The analysis ofc2 showed that the segregation ratio of this population was consistent with the segregation ratio 3:1,indicating that inheritance of leaf-color ofz1was single gene dominant inheritance pattern.The purple leaf gene PL（Purple leaf）was located between the pSSR020 and CaES177 markers on the chromosome 9 of the pepper by gene location technology.A total of 95 genes were identified in the objective region,and a gene encoding phenylalanine aminotransferase（PAL）（LOC107843092）was found in the vicinity of the CaES177 marker.This gene（CaPAL）has the highest expression level in theleavesof mutant z1 and is a structural gene of the anthocyanin metabolic pathway.3.Silencing of CaPAL resulted in leaf fading of purple leaf mutant z1 and increased z1 sensitivity to low temperature.The silencing vector of TRV2:CaPALwas transformed into the purple leaf mutant z1 by virus-induced gene silencing.The result showed thatCaPAL silencing weakened anthocyanins synthesis and resulted in fading of purple leaves inz1.After low temperature treatment,the leaf-color ofCaPAL silenced pepper was not recovered,and the leaves were curled.In addition,the photosynthetic capacity was weakened,and further the PAL activity,anthocyanin level as soon as activitiesof antioxidant enzymes were also significantly reduced in CaPAL silenced peppers.4.The yellow-leafed inheritance of mutantbmy is controlled partially by cytoplasm,and the ratio of chlorophyll and anthocyanin affects photosynthesis and whitefly resistance.The B12,z1 and bmy were used to perform the reciprocal cross test,and the leaf color of the F1 generation（F1-1F1-6,F1-9）was investigated.The offspringofbmy showed obvious mosaic leaf color and no fixed separation ratio,indicating bmy leaf color was controlled partly by cytoplasmic gene.Among 7 strains,mosaic leaf-color of 3 strain was observed.yellow-green color ofF1-2 and F1-4 leaves;purple-green color F1-3 leaves;purple-yellow colorF1-6 leaves.The leaf photosynthetic rate and root vigor of the purple leaf family（F1-3,F1-6 and F1-9）were higher than those of other families.Among them,the net photosynthetic rate was the highest in F1-3 family.Similar results were also observed in the whitefly resistance,and the resistance of F1-3 strain was highest.This indicates thatexcessive anthocyanins accumulation was helpful for enhancing photosynthetic capacity and resistance to whitefly,improvement of photosynthetic capacity and resistance to whitefly was affected by the ratio of anthocyanin and chlorophyll... |
