| Tomato yellow leaf curl China virus(TYLCCNV)was first described from Guangxi province of China.It belongs to Old-World group of begomoviruses and causes severe crop damages in tobacco,tomato and papaya.TYLCCNV in southern China,is known to infect tobacco and tomato,causing leaf curl and yellow leaf curl disease respectively.Tobacco and tomato species upon agroinoculation with TYLCCNV develop typical leaf curling and yellowing symptoms.TYLCCNV is associated with betasatellite which encodes a protein called?C1.TYLCCNV-?C1 protein is capable of inducing typical begomovirus-like symptoms including leaf enation,yellowing,curling and vein thickening.Also,?C1 is known to interact with host factors and consequently affects host developmental and defense-related responses.In compatible plant-virus interactions,viruses affect transcriptome,proteome,metabolome and morphology/physiology-related abnormalities.The common biochemical and physiological variations include inhibition of photosynthesis,increased respiration,expansion of oxidase activities and accumulation of nitrogenous compounds.Virus-induced key alterations of plant's photosynthetic machinery include:modification of chloroplast's ultrastructure,attachment of viral replication complexes or proteins with chloroplasts and interactions of these viral proteins with chloroplast/photosynthesis related proteins.Since virus-infected plants undergo several physiological and molecular changes even before the development of visible disease symptoms,it is important to study these variations to better understand the underlying events that facilitate the development of disease symptoms.To elucidate the effect of TYLCCNV infection and?C1 on plants'photosynthesis,we measured the relative chlorophyll content and chlorophyll fluorescence.The results showed that chlorophyll content was reduced in both TYLCCNV A+?-infected and?C1 transgenic N.benthamiana plants.Further,the changes in chlorophyll fluorescence parameters(ETR,F_v/F_m,NPQ and qP)revealed compromised photosynthetic efficiency in N.benthamiana under the impact of?C1.Interestingly,changes in chlorophyll fluorescence parameters,particularly for NPQ,were observed at early stage of viral infection.NPQ dynamics in the pathogen-invaded leaf tissues represent disease/pathogenesis signature and have correlation with symptoms development.Thus,during the viral infection,elevation of NPQ might reflect defense-related responses of the host aimed at delayed photoinhibition before establishment of the final infection.Inhibition of photosynthesis might be due to a reduced/altered level of downstream enzyme(s)during plant-virus interaction.Since not much work has been done on photosystem II(PSII)extrinsic proteins,we selected four genes(PsbO,PsbP,PsbQ and PsbR)that comprise the oxygen-evolving complex(OEC).Additionally,we selected PsbS,another PSII subunit of PSII which plays critical role in the activation and regulation of NPQ in thylakoids.The possible variations in accumulation of mRNAs of these genes were investigated by RT-qPCR analysis.Results revealed that the relative expressions of OEC genes were significantly decreased at 14 dpi,though it remained unchanged at 5dpi.Similar trend of reduced mRNA expression was observed in N.benthamiana plants having transgenic expression of?C1.On the other hand,the expression of PsbS in betasatellite-infected plants was significantly higher at 5 dpi and slightly reduced at 14 dpi.Moreover,the expression of PsbS in the seedlings of wild type and?C1-transgenic N.benthamiana remained unchanged however,at vegetative growth stage?C1-transgenes exhibited a significnatly higher expression of PsbS.Next,we performed Y2H assay to investigate whether these physiological and molecular changes were resulting from direct association of?C1 with one or more PSII extrinsic proteins.The results revealed that PsbP positively interacted with?C1 in yeast.Further downstream verification of this interaction is important to elaborate the possible role of viral/host factors in the disease development.Thus,this study improves our understanding of the TYLCCNV-mediated reduction of photosynthetic efficiency in N.benthamiana and elaborates the damaging role of?C1 that not only aggravates the impairment of photosynthesis,but also reduces the expression of OEC genes. |
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