Abstract
Geminiviruses (family Geminiviridae) are plant viruses with small circular single-stranded DNA genomes (mono- or bipartite) encapsidated in geminate virions and transmitted by insect vectors in a persistent circulative manner, causing devastating crop diseases globally. In the Mediterranean, the monopartite geminivirus Tomato yellow leaf curl virus (TYLCV, genus Begomovirus), and invasive recombinants, all transmitted by the whitefly Bemisia tabaci, severly impact tomato and vegetable yields. Recently, bipartite begomoviruses like Tomato leaf curl New Delhi virus (ToLCNDV), prevalent in India and East Asia, have also been detected in the Mediterranean. In a collaborative project funded by the Indo- French foundation CEFIPRA and the Occitanie foundation RIVOC, we investigate mechanisms of circulative transmissions of TYLCV and ToLCNDV by invasive whitefly species, Middle East Asia Minor 1 (MEAM1) and Mediterranean (MED). Effective control of geminiviruses is targeted to their insect vectors, necessitating a thorough understanding of virus circulation and potential replication within the vectors. Our research employs Nanopore sequencing, transcriptomics, and small RNA-omics to study viral DNA replicative forms, viral transcripts, and small RNAs in MED and MEAM1 whiteflies transmitting monopartite versus bipartite begomoviruses. We use a virus-induce gene silencing (VIGS) approach, in which begomovirus betasatellite-based VIGS vectors were designed carrying inserts of the candidate plant and insect genes. Plants infected with helper begomovirus and betasatellite VIGS constructs targeting plants and insect genes are used as source plants for virus acquisition by the whitefly, followed by transmission tests. Initial tests confirmed the efficient replication and transmission of empty VIGS constructs. Subsequenlym silencing the plant PCNA gene led to severe developmental abnormalities, indicating its role in DNA replication. On-going experiments, aim to silence the whitefly PCNA gene and two other genes implicated in begomovirus transmission. The ultimate goal is to develop new strategies to control viral disease spread at the transmission step without affecting insect viability.