Apoptosis in a Whitefly Vector Activated by a Begomovirus Enhances Viral Transmission

Abstract

Of the approximately 1,100 known plant viruses, about one-third are DNA viruses that are vectored by insects. Plant virus infections often induce cellular and molecular responses in their insect vectors, which can, in many cases, affect the spread of viruses. However, the mechanisms underlying vector responses that affect virus accumulation and transmission are poorly understood. Here, we examined the role of virus-induced apoptosis in the transmission of begomoviruses, a group of single-stranded plant DNA viruses that are transmitted by whiteflies and cause extensive damage to many crops worldwide. We demonstrated that virus infection can induce apoptosis in the insect vector conferring protection to the virions from degradation, leading to enhanced viral accumulation and transmission to host plants. Our findings provide valuable clues for designing new strategies to block the transmission of insect-vectored plant viruses, particularly plant DNA viruses.

ABSTRACT

Apoptosis is generally considered the first line of defense against viral infection. However, the role of apoptosis in the interactions between plant viruses and their insect vectors has rarely been investigated. By studying plant DNA viruses of the genus Begomovirus within the family Geminiviridae, which are transmitted by whiteflies of the Bemisia tabaci species complex in a persistent manner, we revealed that virus-induced apoptosis in insect vectors can facilitate viral accumulation and transmission. We found that infection with tomato yellow leaf curl virus activated the apoptosis pathway in B. tabaci. Suppressing apoptosis by inhibitors or silencing caspase-3 significantly reduced viral accumulation, while the activation of apoptosis increased viral accumulation in vivo. Moreover, the positive effect of whitefly apoptosis on virus accumulation and transmission was not due to its cross talk with the autophagy pathway that suppresses begomovirus infection in whiteflies. We further showed that viral replication, rather than the viral coat protein, is likely the critical factor in the activation of apoptosis by the virus. These novel findings indicate that similarly to many animal and a few plant RNA viruses, plant DNA viruses may activate apoptosis in their insect vectors leading to enhanced viral accumulation and transmission.

IMPORTANCE Of the approximately 1,100 known plant viruses, about one-third are DNA viruses that are vectored by insects. Plant virus infections often induce cellular and molecular responses in their insect vectors, which can, in many cases, affect the spread of viruses. However, the mechanisms underlying vector responses that affect virus accumulation and transmission are poorly understood. Here, we examined the role of virus-induced apoptosis in the transmission of begomoviruses, a group of single-stranded plant DNA viruses that are transmitted by whiteflies and cause extensive damage to many crops worldwide. We demonstrated that virus infection can induce apoptosis in the insect vector conferring protection to the virions from degradation, leading to enhanced viral accumulation and transmission to host plants. Our findings provide valuable clues for designing new strategies to block the transmission of insect-vectored plant viruses, particularly plant DNA viruses.