Fourth International Bemisia Workshop International Whitefly Genomics Workshop
A knottin-like putative antimicrobial gene family in the whitefly Bemisia tabaci biotype B: Cloning and transcript regulation
1 Subtropical Insects Research Unit, U. S. Horticultural Research Laboratory, ARS, USDA, Fort Pierce, FL USA. Correspondence: rshatters@ushrl.ars.usda.gov
2 The Robert H. Smith Institute for Plant Science and Genetics in Agriculture, The Hebrew University of Jerusalem, Rehovot, Israel
3 IRREC, IFAS, University of Florida, Fort Pierce, FL USA
4 Department of Plant Sciences, The University of Arizona, Tucson, AZ, USA
The whitefly, Bemisia tabaci, is a worldwide plant pest and the vector of agriculturally important plant pathogenic begomoviruses. Of two vectored begomoviruses, Tomato yellow leaf curl virus (TYLCV) is transcriptionally active in B. tabaci and Tomato mottle virus (ToMoV) is not. Comparative analyses of 7093 EST sequences from cDNA libraries from either aviruliferous or ToMoV or TYLCV viruliferous whiteflies revealed four clones of a knottin-like gene family (btk-1, -2, -3, and -4). Two of these, btk-1 and btk-3, were more abundant in cDNA libraries from viruliferous whiteflies. Time course, virus uptake/acquisition experiments showed physical manipulation of whiteflies induced a transient increase in btk-1and btk-3 transcripts that was influenced by the presence of ToMoV. The Btk proteins range from 59 to 65 amino acids, and contain a secretory signal sequence and a conserved spatial representation (in peptide sequence and predicted 3-D protein-folding model) of six cysteine residues. These characteristics were identical to those for plant and insect knottin-family antifungal/toxin proteins. Begomovirus ingestion and physical stress influence on transcript abundance and sequence similarities with other knottin proteins suggest that btk protein family belongs to the knottin antimicrobial family and are part of the insect innate immune system.