Studies on the interaction of viruses and their plant hosts: Transmission in seed and symptom determinants

Scope and method of study. This study was carried out to investigate the interaction between selected viruses and their plant hosts related to seed transmission and symptom induction. The mechanism of virus seed transmission was investigated using Arabidopsis thaliana infected with turnip yellow mosaic tymovirus (TYMV) and/or tobacco mosaic tobamovirus (TMV). Protein A---enzyme-linked immunosorbent assay (PAS-ELISA) and grow-out tests were used to evaluate seed transmission. Sexual crosses between healthy and virus infected A. thaliana were conducted to determine the route of TYMV and TMV leading to virus establishment in the developing seed. Investigation on the genetic determinant for symptom attenuation of the mild strain of cowpea chlorotic mottle bromovirus (CCMV-M) was done by using infectious in vitro, transcripts derived from RNA 3 cDNA clones of chimeric viruses constructed by exchanging restriction fragments between CCMV-M and the type strain (CCMV-T).; Findings and conclusions. Both TYMV and TMV invaded seed of A. thaliana however only TYMV was seed-transmitted. The transmission of TYMV in seed of A. thaliana is linked to the embryo infection by the virus. Grow-out tests are more accurate than ELISA in determining the amount of transmission. Further investigation through crosses of healthy and virus infected plants indicated that TYMV, but not TMV, was carried by pollen into the embryo-sac from where it reached the embryo. Comparison of nucleotide sequences of CCMV strains M and T revealed four base changes. In vitro transcripts of chimeric CCMV RNA 3 cDNA clones containing these changes individually showed that the genetic determinant of symptom expression is located in the 3' portion of the coat protein gene.