Cinnamoyl coA:NADP oxidoreductase like 1 regulates abscisic acid response by modulating phaseic acid homeostasis in Arabidopsis thaliana.

Phaseic acid (PA), a main catabolite of abscisic acid (ABA), is structurally related to ABA and possesses ABA-like hormonal activity. However, the comprehensive metabolism pathway and roles of PA is not well understood. Here, we identified the previously named CRL1 (Cinnamoyl coA:NADP oxidoreductase like 1) as a PA reductase that catalyzes PA to dihydrophaseic acid (DPA) via a homologous alignment and expression pattern analysis strategy in Arabidopsis. The function of CRL1 and the potential role of PA were studied in the genetically transgenic material of CRL1. Overexpression of CRL1 (OE) resulted in decreased ABA sensitivity in seed germination and attenuated drought tolerance. In contrast, increased ABA sensitivity and elevated drought tolerance was observed in down-regulated and loss-of-function crl1 mutants. The Tyr162 residues in the conserved motif of CRL1 is key to the PA catalytic activity. Accelerated seed germination and earlier flowering phenotype was also observed in OE lines, while retarded seed germination and delayed flowering time in crl1 mutants which accumulated more PA while less DPA than the wildtype (WT). This study demonstrates that PA plays diverse functions in plant including drought tolerance, seed germination and flowering in an ABA-like manner, which may expand the plant adaptive plasticity.