Effect On Chlorophyll Metabolism In Lemon,pummelo And Sweet Orange By Citrus Yellow Vein Clearing Virus

Citrus yellow vein disease,caused by Citrus yellow vein clearing virus,is an emerging viral disease in China.It has caused devastating losses in Chinese lemon production.Some typical leaf symptoms include yellow vein clearing,chlorosis,leaf distortion were observed on CYVCV-infected Eureka lemon.Furthermore,CYVCV could produce mild to severe vein clearing and chlorisis in the young leaf of other citrus cultivars.Until now,the mechanism of symptom by CYVCV has not yet been elucidated.In this study,Eureka lemon(Citrus limon(L.)Burm.F.cv.Eureka),Guanximiyou pummelo(C.grandis.cv.Guanximiyou)and Symons sweet orange(C.sinensis(L.)Osbeck.cv.Symons)were addressed to investigate the effect of CYVCV infection on chlorophyll metabolism.The contents of chlorophyll and key precursors of chlorophyll biosynthesis,chlorophyll metabolism-related key enzymes activities were analyzed.Furthermore,the expression levels of CYVCV and chlorophyll metabolism-related key genes were detected by using real-time PCR.Main results are shown as follows:1.The relative accumulations of CYVCV in Symons sweet orange were the highest,followed by Eureka lemon and Guanximiyou pummelo.The result suggested that the amounts of CYVCV were not associated with the symptom in different citrus cultivars.The contents of chlorophyll in spring shoot,summer shoot and autumn shoot of CYVCV-infected Eureka lemon,as well as in spring shoot of CYVCV-infected Guanximiyou pummelo were significantly decreased,whereas the contents of chlorophyll had no significant changes in summer shoot and autumn shoot of CYVCV-infected Guanximiyou pummelo,as well as in spring shoot,summer shoot and autumn shoot of CYVCV-infected Symons sweet orange.The loss of chlorophyll caused by CYVCV and the amounts of CYVCV were greatly inhibited by high temperature in summer.2.The contents of δ-aminolevulinic acid,porphobilinogen,uroporphyrinogen III and coproporphyrinogen III in spring shoot,summer shoot and autumn shoot of CYVCV-infected Eureka lemon were significantly increased,whereas the contents of protoporphyrin IX,Mg-protoporphyrin IX and protochlorophyllide were decreased significantly.The contents of protoporphyrin IX,Mg-protoporphyrin IX and protochlorophyllide in spring shoot of CYVCV-infected Guanximiyou pummelo were decreased significantly.The results suggested that the chlorophyll biosynthesis was blocked by CYVCV at the step from coproporphyrinogen III to protoporphyrin IX in spring shoot,summer shoot and autumn shoot of CYVCV-infected Eureka lemon and spring shoot of CYVCV-infected Guanximiyou pummelo.The contents of chlorophyll synthesis precursors in spring shoot,summer shoot and autumn shoot of CYVCV-infected Symons sweet orange,as well as in summer shoot and autumn shoot of CYVCV-infected Guanximiyou pummelo had no significant changes.3.The activities of protoporphyrinogen IX oxidase and Mg-chelatase in spring shoot,summer shoot and autumn shoot of CYVCV-infected Eureka lemon,as well as in spring shoot of CYVCV-infected Guanximiyou pummelo were significantly decreased,whereas the activities of chlorophyllase were increased significantly.The results inferred that the decrease of chlorophyll was caused by block of chlorophyll synthesis and accelerating degradation of chlorophyll.Furthermore,the activities of δ-aminolevulinate dehydratase,porphobilinogen deaminase and coproporphyrinogen III oxidase in spring shoot and autumn shoot of CYVCV-infected Eureka lemon,which may be one of the reason why chlorophyll decreased most greatly in Eureka lemon.The activities of related enzymes involved in chlorophyll metabolism in spring shoot,summer shoot and autumn shoot of CYVCV-infected Symons sweet orange,as well as in summer shoot and autumn shoot of CYVCV-infected Guanximiyou pummelo had no significant changes.4.The expression levels of related genes involved in chlorophyll metabolism in Eureka lemon and Guanximiyou pummelo showed the same change tendency with their enzymes activities.Especially,the chlorophyll synthesis related genes HEMG and CHLH down-regulated significantly in spring shoot,summer shoot and autumn shoot of CYVCV-infected Eureka lemon,as well as in spring shoot of CYVCV-infected Guanximiyou pummelo,whereas the chlorophyll degradation related genes CLH up-regulated significantly.The expression levels of most of related genes involved in chlorophyll metabolism in Symons sweet orange had no significant changes.