Diana Leibman
The Volcani Center, Israel
Title: The various roles of CsRDR1 family genes in cucumber defense against different viruses
Biography
Biography: Diana Leibman
Abstract
RNA-dependent RNA polymerases (RDR) play an important role in virus protection and plant gene control. Their activity is based on the synthesis of double stranded RNA that is a template for the gene silencing system. Four RDR1 (RDR1a, b, c1, c2) genes were identified in cucumber having different expression levels before and after infection by various viruses. The CsRDR1a, b, c genes have a homology of 60-58% at the amino acid level, while CsRDR1c1 and c2 are almost identical (97% homology), but have different promoter sequences. A high expression level of CsRDR1b was characterized in cucumber strains with partial resistance to a number of viruses, while CsRDR1c1 and c2 not expressed in healthy plants. Cucumber plants infected by several different viruses showed a moderate expression level of CsRDR1b and a dramatic level of CsRDR1c1, c2. The expression level of CsRDR1a, CsRDR2 and CsRDR6 did not increase following virus infection. The differential expression of CsRDR1b and CsRDR1c1, c2 indicates dissimilar control of these genes. The relationship between the high levels of expression of CsRDR1b in resistant cucumber cultivars reinforces the assumption that this gene is unique for virus resistance. Using the CRISPR/Cas9 system, we created a variety of mutants in the rdr1b and rdr1c1 and c2 genes. Knockdown of these genes increased virus accumulation. Plants with a homozygous mutation in the rdr1b genes (deletion of 34 nucleotides) and rdr1c (2 and 1 nucleotides in the rdr1c1 and rdr1c2 genes respectively) showed increased susceptibility to Cucumber mosaic virus 4 dpi, especially rdr1c mutants plants which collapse 6 days after infection. The viral symptoms increased also after Cucurbit vein yellowing virus infection, whereas the susceptibility to Zucchini yellow mosaic virus infection was less. Notably, CsRDR1b expression in healthy rdr1b mutants was less than in non-mutant plants. The control of CsRDR1b and CsRDR1c1, c2 is under study in our laboratory to help understand the silencing mechanism of plants defense.