Cyclic GMP mediates abscisic acid-stimulated isoflavone synthesis in soybean sprouts

The influences of abscisic acid (ABA)-guanosine 3',5'-cyclic monophosphate (cGMP) on UV-B treatment-stimulated isoflavone synthesis in soybean sprouts was explored. It turned out that ABA, with cGMP, up-regulated gene expression and activity of chalcone synthase (CHS) and isoflavone synthase (IFS), and subsequently induced isoflavone biosynthesis under UV-B treatment. Furthermore, data obtained from the isobaric tags for relative and absolute quantification (iTRAQ) analysis showed that there were two core components in ABA response: SNF1-related protein kinase (SnRK) and type 2C protein phosphatase (PP2C), were up and down regulated after UV-B treatment, respectively. UV-B exposure stimulated increment in guanine nucleotide-binding protein and calreticulin expression. Additionally, CHS and IFS protein expression were up regulated under UV-B stress. Overall, UV-B-induced ABA resulted in PP2C inhibition and SnRK2 activation, and up-regulated CHS and IFS expression, leading to enhancement of isoflavone accumulation. cGMP and calreticulin as downstream messengers, mediated ABA-stimulated isoflavone biosynthesis after UV-B exposure.