Trans-acting small interfering RNA4: key to nutraceutical synthesis in grape development?

• Evolution of TAS4 important for eudicot fitness, possibly driven by animal frugivory.
• A TAS4 siRNA targets two novel grape MYBs important for nutraceutical biosynthesis.
• Transitivity of TAS4- and miR828-targeted MYBs suggests a master regulatory role.
• MYB targets of TAS4 are potential effectors of fruit development and microbial disease symptoms.
• Biotech applications of TAS4 have potential for healthier foods and biomass feedstocks.

The facility and versatility of microRNAs (miRNAs) to evolve and change likely underlies how they have become dominant constituents of eukaryotic genomes. In this opinion article I propose that trans-acting small interfering RNA gene 4 (TAS4) evolution may be important for biosynthesis of polyphenolics, arbuscular symbiosis, and bacterial pathogen etiologies. Expression-based and phylogenetic evidence shows that TAS4 targets two novel grape (Vitis vinifera L.) MYB transcription factors (VvMYBA6, VvMYBA7) that spawn phased small interfering RNAs (siRNAs) which probably function in nutraceutical bioflavonoid biosynthesis and fruit development. Characterization of the molecular mechanisms of TAS4 control of plant development and integration into biotic and abiotic stress- and nutrient-signaling regulatory networks has applicability to molecular breeding and the development of strategies for engineering healthier foods.