The Specialized Roles in Carotenogenesis and Apocarotenogenesis of the Phytoene Synthase Gene Family in Saffron

Abstract

Crocus sativus stigmas are the main source of crocins, which are glucosylated apocarotenoids derived from zeaxanthin cleavage that give saffron its red color. Phytoene synthase (PSY) mediates the first committed step in carotenoid biosynthesis in plants. Four PSY genes encoding functional enzymes were isolated from saffron. All the proteins were localized in plastids, but the expression patterns of each gene, CsPSY1a , CsPSY1b , CsPSY2 , and CsPSY3 , in different saffron tissues and during the development of the stigma showed different tissue specialization. The CsPSY2 transcript was primarily detected in the stigmas where it activates and stimulates the accumulation of crocins, while its expression was very low in other tissues. In contrast, CsPSY1a and CsPSY1b were mainly expressed in the leaves, but only CsPSY1b showed stress-light regulation. Interestingly, CsPSY1b showed differential expression of two alternative splice variants, which differ in the intron retention at their 5′ UTRs, resulting in a reduction in their expression levels. In addition, the CsPSY1a and CsPSY1b transcripts, together with the CsPSY3 transcript, were induced in roots under different stress conditions. The CsPSY3 expression was high in the root tip, and its expression was associated with mycorrhizal colonization and strigolactone production. CsPSY3 formed a separate branch to the stress-specific Poaceae homologs but was closely related to the dicot PSY3 enzymes.

UGT709G1: a novel uridine diphosphate glycosyltransferase involved in the biosynthesis of picrocrocin, the precursor of safranal in saffron (Crocus sativus)

“…To produce transient transgenic plants in which green fluorescent protein (GFP)-tagged UGT709G1 was expressed under the con-troCheck supplier details setl of the 35S promoter, the GoldenBraid (GB) strategy was used as previously described (Ahrazem et al, 2019). The amplified fragment was introduced into the pUPD2 vector, and from this vector to pDGB3Ω1-GFP.…”

“…The agroinfiltrated leaves were analyzed 3-5 d following infiltration, as previously described (Ahrazem et al, 2019). For GFP detection, the excitation source was an argon-ion laser at 488 nm, and emission was observed between 510 and 530 nm.…”

“…1; Cazzonelli & Pogson, 2010). We have recently shown the existence of three PSYs in saffron, each showing a tissue-specific role in leaf (PSY1a/ b), stigma (PSY2), and root (PSY3) carotenoid, apocarotenoid, and strigolactone synthesis, respectively (Ahrazem et al, 2019). Phytoene undergoes consecutive modifications, such as desaturation and isomerization, to form lycopene, which represents the first branch point of the carotenoid pathway.…”

Comparative analysis of structural and functional aspects of phytoene synthase from Meiothermus taiwanensis strain RP

“…Phytoene synthases have directly evolved from bacteria to plants through various bacterial taxonomic groups and algae (Sandmann 2002 (Zhao et al 2011). A chaperone protein named Orange protein has been reported to help in the stability of phytoene synthases in many plants (Ahrazem et al 2019); no PSY stabilizing protein in bacteria has been reported so far.…”

“…The differences in localization, internal environmental conditions, the presence/absence of introns(Dibari et al 2012;Ahrazem et al 2019), and the presence/absence of signal peptides(Kadono et al 2015) might be the reason for the variation in sequence length among the different PSY proteins.The instability index of Meiothermus taiwanensis strain RP sequence is 31.09, which is well below the value of 40, above which proteins are deemed to be unstable. Thus, the RP PSY protein is stable in nature.…”