Cucumber RDR1s and cucumber mosaic virus suppressor protein 2b association directs host defence in cucumber plants

Abstract

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

“…We have recently shown that the CMV-2b suppressor protein was associated with induction of CsRDR1c expression [ 36 ]. In light of this, we examined the expression level of CmRDR1c1 and CmRDR1c2 separately in melon infected with CMV and the CMV-Δ2b mutant.…”

“…In CMV-infected melon, CmRDR1a gene expression was induced 21-fold, but not by Potyviridae (ZYMV and CVYV) and a tobamovirus (CGMMV) ( Figure 5 and Figure 7 ). Likewise, in cucumber protoplasts, transfection with CMV increased CsRDR1a expression level 29-fold and exogenous application of CsRDR1a reduced CMV accumulation dramatically [ 36 ], probably due to 2b induction [ 36 ]. However, the involvement of CmRDR1a in defense against potyviruses needs additional study.…”

“…However, CMV with a deleted 2b gene induced significantly lower CmRDR1c1+2 transcript accumulation (about 10 to 15-fold lower) ( Figure 5 ), which may indicate that CmRDR1c1+2 gene expression was regulated by CMV level. Alternatively, the 2b protein can enter the nucleus [ 22 ] and can elicit PAMP-triggered immunity [ 36 , 48 ]. In addition, in melon infected with the tobamovirus CGMMV, CmRDR1c1+2 expression was induced ~100 fold, probably because of the high level of CGMMV-CP accumulation, an oxidative burst inducer as demonstrated in tobacco by tobacco mosaic virus [ 49 ] or via tobacco mosaic virus dsRNA inducer molecules [ 50 ].…”

“…This change may reflect the difference between the suppressors of these genera (P1b of CVYV versus the potyvirus HCPro) [ 51 ]. Notably, expression of other RDR genes ( CmRDR2 and CmRDR6 ) was induced in melon by CMV infection, but not by potyviruses and tobamovirus, which suggests that the suppressor 2b of CMV may play a role in PAMP-triggered immunity [ 36 ].…”

“…In addition, CmRDR1c1+2 were highly expressed in WT plants compared with very low levels of expression in mutant plants, suggesting rapid degradation of aberrant RDR1c1 and c2 transcripts of the nonfunctional proteins [ 43 ]. These data suggest that CmRDR1c1 and CmRDR1c2 are unique genes associated with defense against CMV infection specifically, and the virus–host interaction in cucumber between the inducer 2b and RDR1c1+c2 probably also occurs in melon [ 36 ]. Such virus-specific protection has not been reported.…”