The plant hormone abscisic acid (ABA) intricately regulates a multitude of processes during plant growth and development. Recent studies have established a connection between genes participating in various steps of cellular RNA metabolism and the ABA signal transduction machinery. In this chapter we focus on the plant nuclear mRNA cap binding proteins, CBP20 and CBP80. We summarize and report recent findings on their effects on cellular signal transduction networks and mRNA processing events. ABA hypersensitive 1 (abh1) harbors a gene disruption in the Arabidopsis CBP80 gene. Loss-of-function mutation of ABH1 can also result in an early flowering phenotype in the Arabidopsis accession C24. abh1 revealed noncoding cis-natural antisense transcripts (cis-NATs) at the CONSTANS locus in wild-type plants with elevated cis-NAT expression in the mutant. abh1 also revealed an influence on the splicing of the MADS box transcription factor Flowering Locus C pre-mRNA, which may result in the regulation of flowering time. Furthermore, new experiments analyzing complementation of cpb20 with site-directed cpb20 mutants provide evidence that the CAP binding activity of CBP20 is essential for the observed cbp-associated phenotypes. In conclusion, mutants in genes participating in RNA processing provide excellent tools to uncover novel molecular mechanisms for the regulation of RNA metabolism and of signal transduction networks in wild-type plants.