Integration of apocarotenoid and transcriptome profiles of developing stigmas of saffron (Crocus sativus L.) reveals a multifaceted control involving PSY2, OR-a, PIF1 and HY5 genes in regulation of apocarotenoid biosynthesis

Integration of the apocarotenoid and transcriptome profiles in developing stigmas of saffron revealed a biphasic pattern of carotenoid biosynthetic pathway. While the synthesis of lycopene peaks at S2 stage that of β- carotene and CsLCY-β, peaks at S3 stage of stigma development. CsZCD, CsGTF, CsBGSD, CsADH and CsVDE, responsible for the oxidative cleavage of carotenoids to produce apocarotenoids, showed highest expression in S4 stage stigmas. CsPSY2, CsBCH and CsCCD2 showed the highest correlation with apocarotenoid accumulation in the stigmas, indicating them to be the key genes in carotenoid biosynthesis. Our results indicate active plastid development in yellow and orange stigmas and active chromoplast differentiation in red (S3) and scarlet (S4) stigmas. The expression of the OR-a gene in the stigmas was found to be strongly related to chromoplast biogenesis. On the basis of correlation networking, we suggest the involvement of a repression-activation transcriptional complex comprised of the CsPIF1, CsHY5 and CsPSY2 genes in regulating the biosynthesis of carotenoids in the saffron stigmas.