Role Of Apoptosis In The Interactions Between Whitefly And Tomato Yellow Leaf Curl Virus And The Underlying Mechanisms

The whitefly Bemisia tabaci(Gennadius)(Hemiptera:Aleyrodidae)is a cryptic species complex,consisting of more than 39 morphologically indistinguishable cryptic species.Whiteflies damage crops by direct feeding and vectoring multiple plant viruses.So far,knowledge with regard to the detailed mechanisms underlying whitefly transmission of plant viruses remain largely unknown,thus hindering research and development of new technology for the control of these plant viruses.Apoptosis is the autonomous death process of cells and controlled by related genes to maintain organism homeostasis.Apoptosis,as a type of eukaryotic conserved pathway that responds to external stimuli,plays an important role in the regulation of insect development and defense against pathogen infection.In this study,we investigated the role of apoptosis in the interactions between whitefly and tomato yellow leaf curl virus(TYLCV)and the underlying mechanisms.We employed a comprehensive genomics approach to identity caspases in B.tabaci Middle East Asia Minor 1(MEAM1),an invasive whitefly species that is devastating to the production of many crops.Four caspase genes(Bt-caspase-1?Bt-caspase-3a?Bt-caspase-3b?Bt-MALT-1)were identified,and their motif compositions were predicted.Structures were relatively conserved in both putative effector and initiator caspases.Expression patterns of caspase genes differed across insect developmental stages.Three caspase genes were induced immediately after ultraviolet(UV)treatment.Expression levels of Bt-caspase-1 and Bt-caspase-3b increased in the midgut and salivary glands during apoptosis induced by UV treatments,whereas silencing both genes reduced UV-triggered apoptosis.Our study demonstrates that Bt-caspase-1 and Bt-caspase-3b act as putative initiator and effector of apoptotic caspases in the ME AM1 whitefly,respectively.We found that infection of B.tabaci with TYLCV can activate its apoptosis pathway.Whiteflies were fed on TYLCV infected tomato for 24 hours and then transferred to cotton for 120 hours,we used different methods,such as qPCR,Western Blot,TUNEL and TEM,to prove that apoptosis is activated in whitefies.Suppressing apoptosis with chemical inhibitors or silencing caspase-3 significantly decreased viral accumulation,while activation of apoptosis increased viral accumulation in vivo indicating that virus-induced apoptosis in insect vectors can facilitate viral accumulation and transmission.In conclusion,these results contribute to a better understanding of the role of apoptosis in the whitefly transmission of plant viruses.Our findings provide new information for developing novel technololgy against insect-borne plant viruses.