Proceedings of the XLV Italian Society of Agricultural Genetics - SIGA Annual Congress

Salsomaggiore Terme, Italy - 26/29 September, 2001

ISBN 88-900622-1-5

Poster Abstract

TRANSGENICALLY EXPRESSED T-REP OF TOMATO YELLOW LEAF CURL SARDINIA VIRUS HAS A DUAL ROLE IN VIRUS RESISTANCE

BRUNETTI A.*, TAVAZZA R.*, NORIS E.**, LUCIOLI A.*, ACCOTTO G.P.**, TAVAZZA M.*

*ENEA, Divisione Biotecnologie e Agricoltura, C.R. Casaccia, Roma, Italy

** Istituto di Fitovirologia Applicata, CNR, Torino, Italy

The C1 gene of begomoviruses encodes a multifunctional replication associated protein (Rep) which is involved in viral replication and autoregulation of its own gene transcription. The C1 gene contains in a different frame the small ORF C4. The C4 protein has been involved in viral movement and/or down-regulation of C1 transcription. We have previously shown that transgenic Lycopersicon esculentum and N. benthamiana plants expressing a truncated form of the Rep protein (T-Rep) of tomato yellow leaf curl Sardinia begomovirus (TYLCSV) and potentially coexpressing the C4 protein are resistant to TYLCSV. In the present study we have investigated the role of T-Rep and the C4 protein in the resistance mechanism, analysing changes in virus transcription and replication. Transgenic N. benthamiana plants and protoplasts were challenged with TYLCSV and the related TYLCSV Murcia strain (TYLCSV-ES[1]). Transgenic plants were susceptible to TYLCSV-ES[1], moreover TYLCSV but not TYLCSV-ES[1] replication was strongly inhibited in transgenic protoplasts as well as in wild-type (wt) protoplasts transiently expressing T-Rep but not the C4 protein. New viral DNA forms were consistently observed in transgenically and transiently T-Rep expressing protoplasts. Biochemical studies showed that these DNAs were partial duplexes with the minus strand incomplete. Interestingly, similar viral DNAs were also found at early stages of TYLCSV replication in wt N. benthamiana protoplasts. Transgenically expressed T-Rep repressed the transcription of the GUS reporter gene up to three hundred fold when fused to the homologous (TYLCSV) but not to the heterologous (TYLCSV-ES[1]) C1 promoter. Similarly, transiently expressed T-Rep but not C4 protein strongly repressed GUS transcription when fused to the C1 promoter of TYLCSV. A model of T-Rep interference with TYLCSV transcription-replication is proposed.