Analysis of the RNA-Dependent RNA Polymerase 1 (RDR1) Gene Family in Melon

Abstract

RNA-dependent RNA polymerase 1 (RDR1) plays a crucial defense role against plant viruses by secondary amplification of viral double-stranded RNA in the gene-silencing pathway. In this study, it was found that melon (Cucumis melo) encodes four RDR1 genes (CmRDR1a, b, c1 and c2) similar to the CsRDR1 gene family of cucumber (C. sativus). However, in contrast to cucumber, melon harbors a truncated CmRDR1b gene. In healthy plants, CmRDR1a was expressed, whereas the expression of CmRDR1c1/c2 was not detected. CmRDR1a expression level increased 20-fold upon cucumber mosaic virus (CMV) infection and was not increased in melon plants infected with zucchini yellow mosaic virus (ZYMV), cucumber vein yellowing virus (CVYV) and cucumber green mottle mosaic virus (CGMMV). The expression of CmRDR1c1/c2 genes was induced differentially by infection with viruses from different families: high levels of ~340-, 172- and 115-fold increases were induced by CMV, CVYV and CGMMV, respectively, and relatively low-level increases by potyvirus infection (4- to 6-fold). CMV mutants lacking the viral silencing suppressor 2b protein did not cause increased CmRDR1c/c2 expression; knockout of CmRDR1c1/c2 by CRISPR/Cas9 increased susceptibility to CMV but not to ZYMV. Therefore, it is suggested that the sensitivity of melon to viruses from different families is a result of the loss of function of CmRDR1b.

Mutagenesis of the melon Prv gene by CRISPR/Cas9 breaks papaya ringspot virus resistance and generates an autoimmune allele with constitutive defense responses

“…In 2022, a handful of papers reported melon knockout lines obtained by CRISPR/Cas9. Two of the targeted genes were involved in fruit ripening ( Giordano et al , 2022 ; Liu et al , 2022 ), the other two affected plant–virus interactions ( Leibman et al ., 2022 ; Pechar et al , 2022 ).…”

Differential Effects of RNA-Dependent RNA Polymerase 6 (RDR6) Silencing on New and Old World Begomoviruses in Nicotiana benthamiana

“…RDR1 and RDR6 are considered major contributors to the post-transcriptional antiviral system [22]. Although RDR1 plays an important role in the antiviral defence of different host plants, including Arabidopsis, tomatoes, tobacco, and potatoes [23][24][25][26], it is nonfunctional in Nicotiana benthamiana due to the presence of a 72 nt insert that generates in-frame stop codons [27,28]. Such impaired RDR1 activity offers unique opportunities to investigate the specific antiviral roles of RDR6 in this host.…”