A Genetic Approach to Abscisic Acid Signaling And RNA Interference In Arabidopsis Embryogenesis

Abscisic acid (ABA) is a plant hormone important for environmental stress responses and embryo development.  RNA interference (RNAi) is a eukaryotic post-transcriptional gene silencing process mediated by endogenous 20- 24 nucleotide small RNAs including microRNAs.  Mutants of the model plant Arabidopsis thaliana such as ABA-hypersensitive1 (abh1) have implicated ABA in microRNA biogenesis and RNA processing, but the molecular mechanisms are unknown.  A  double mutant of abh1 (encodes CAP-BINDING PROTEIN80) and suppressor of gene silencing3 (sgs3, a coiled-coil domain required for RNAi and natural virus resistance) manifests pleiotropic phenotypes such as fused cotyledons, reduced seed set, and reduced susceptibility to fungal infection, suggesting that ABH1 and SGS3 interact genetically, possibly through an ABA signaling pathway.  To test this hypothesis, we are in the process of determining the ABA sensitivity of the abh1/sgs3 double mutant to inhibition of seed germination.  We have shown in dose-response assays that the abh1 mutant seeds are significantly more sensitive to ABA. In order to identify novel components in the ABA signaling/RNAi network, we performed mutagenesis to screen for enhancers and suppressors affecting the phenotypes of abh1/sgs3.  Progress of the mutagenesis and results of ABA sensitivity of the abh1/sgs3 double mutant will be presented.   Establishment of a role for RNAi in ABA-mediated gene regulation, and isolation of new mutants affecting the complex post-transcriptional networks of ABA and RNAi will provide insights into molecular mechanisms of plant growth and development, which in turn may be applicable to genetic engineering of sustainable agriculture in the face of climate change.