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

Area of Science:

• Plant Molecular Biology
• Plant Pathology
• Genetics and Genomics

Background:

• RNA-dependent RNA polymerase 1 (RDR1) is vital for plant antiviral defense through RNA silencing.
• Melon (Cucumis melo) possesses four RDR1 genes (CmRDR1a, CmRDR1b, CmRDR1c1, CmRDR1c2), analogous to cucumber's CsRDR1 family.
• Melon's CmRDR1b gene is notably truncated, unlike its cucumber counterpart.

Purpose of the Study:

• To investigate the role and expression patterns of melon RDR1 genes in response to viral infections.
• To understand the genetic basis for melon's differential susceptibility to various plant viruses.
• To elucidate the contribution of the truncated CmRDR1b gene to plant defense mechanisms.

Main Methods:

• Gene expression analysis of CmRDR1 genes in melon plants under different viral infections (CMV, ZYMV, CVYV, CGMMV).
• Utilizing CRISPR/Cas9 to knock out CmRDR1c1/c2 genes.
• Assessing plant susceptibility to viral infections post-gene knockout.

Main Results:

• CmRDR1a is constitutively expressed and induced by CMV, but not by ZYMV, CVYV, or CGMMV.
• CmRDR1c1/c2 expression is differentially induced by various viruses, with significant increases by CMV, CVYV, and CGMMV.
• Knockout of CmRDR1c1/c2 increased susceptibility to CMV but not ZYMV, and CMV mutants lacking the 2b protein did not induce CmRDR1c/c2 expression.

Conclusions:

• The differential induction of CmRDR1c1/c2 genes suggests a complex, virus-specific antiviral response in melon.
• The loss of function of the truncated CmRDR1b gene is proposed as a key factor in melon's varied sensitivity to different virus families.
• CmRDR1c1/c2 play a role in defense against CMV, mediated by the viral 2b suppressor protein.