An autoregulatory feedback loop involving PAP1 and TAS4 in response to sugars in Arabidopsis

miR828 in Arabidopsis triggers the cleavage of transcripts of Trans-Acting SiRNA Gene 4 (TAS4) and the production of TAS4-derived small interfering RNAs (ta-siRNAs). One such siRNA, TAS4-siRNA81(-), targets the same subset of MYB transcription factors as miR828, specifically PAP1/MYB75, PAP2/MYB90, and MYB113 in the pathway for anthocyanin biosynthesis. We found that PAP1, PAP2, and TAS4 expression are induced specifically by exogenous treatment of sucrose and glucose in Arabidopsis seedlings. The induction is attenuated in the abscisic acid (ABA) signaling pathway mutants, especially in abi3-1 and abi5-1 for PAP1 or PAP2, while no such effect is observed for TAS4 which responds to sucrose in a dose- and time-dependent manner. PAP1 is under regulation by TAS4, supported by the accumulation of PAP1 transcripts and anthocyanin in ta-siRNA biogenesis pathway mutants, while TAS4-siR81(-) expression is increased in pap1-D, an activation-tagged line for PAP1, indicating a feedback regu