Ectopic 5' splice sites inhibit gene expression by engaging RNA surveillance and silencing pathways in plants.

The quality control of mRNA maturation is a highly regulated process that surveys pre-mRNA integrity and eliminates improperly matured pre-mRNAs. In nature, certain viruses regulate the expression of their genes by hijacking the endogenous RNA quality control machinery. We demonstrate that the inclusion of 5' splice sites within the 3'-untranslated region of a reporter gene in plants alters the pre-mRNA cleavage and polyadenylation process, resulting in pre-mRNA degradation, exemplifying a regulatory mechanism conserved between kingdoms. Altered pre-mRNA processing was associated with an inhibition of homologous gene expression in trans and the preferential accumulation of 24-nucleotide (nt) short-interfering RNAs (siRNAs) as opposed to 21-nt siRNA subspecies, suggesting that degradation of the aberrant pre-mRNA involves the silencing machinery. However, gene expression was not restored by coexpression of a silencing suppressor or in an RNA-dependent RNA polymerase (RDR6)-deficient background despite reduced 24-nt siRNA accumulation. Our data highlight a complex cross talk between the quality control RNA machinery, 3'-end pre-mRNA maturation, and RNA-silencing pathways capable of discriminating among different types of aberrant RNAs.