Transcriptome wide identification, characterization and expression analysis of PHD gene family in Crocus sativus.

Crocus sativus L., of the Iridaceae family, yields world's most prized spice, saffron. Saffron is well known for its distinctive aroma, odour and colour, which are imputed to the presence of some specific glycosylated apocarotenoids. Even though the main biosynthetic pathway and most of the enzymes leading to apocarotenoid production have been identified, the regulatory mechanisms that govern the developmental stage and tissue specific production of apocarotenoids in Crocus remain comparatively unravelled. Towards this, we report identification, and characterization of plant homeodomain (PHD) finger transcription factor family in Crocus sativus. We also report cloning and characterisation of CstPHD27 from C. sativus. CstPHD27 recorded highest expression in stigma throughout flower development. CstPHD27 exhibited expression pattern which corresponded to the apocarotenoid accumulation in Crocus stigmas. CstPHD27 is nuclear localized and transcriptionally active in yeast Y187 strain. Over-expression of CstPHD27 in Crocus stigmas enhanced apocarotenoid content by upregulating the biosynthetic pathway genes. This report on PHD finger transcription factor family from C. sativus may offer a basis for elucidating role of this gene family in this traditionally and industrially prized crop. Supplementary Information: The online version contains supplementary material available at 10.1007/s12298-024-01410-3.

Transcriptome wide identification, phylogenetic analysis, and expression profiling of zinc-finger transcription factors from Crocus sativus L.

Crocus sativus belongs to Iridaceae family and is the only plant species which produces apocarotenoids like crocin, picrocrocin, and safranal in significant quantities. Besides their organoleptic properties, Crocus apocarotenoids have been found to possess remarkable pharmacological potential. Although apocarotenoid biosynthetic pathway has been worked out to a great degree, but the mechanism that regulates the tissue and developmental stage-specific production of Crocus apocarotenoids is not known. To identify the genes regulating apocarotenoid biosynthesis in Crocus, transcriptome wide identification of zinc-finger transcription factors was undertaken. 81 zinc-finger transcription factors were identified which grouped into eight subfamilies. C2H2, C3H, and AN20/AN1 were the major subfamilies with 29, 20, and 14 members, respectively. Expression profiling revealed CsSAP09 as a potential candidate for regulation of apocarotenoid biosynthesis. CsSAP09 was found to be highly expressed in stigma at anthesis stage corroborating with the accumulation pattern of apocarotenoids. CsSAP09 was nuclear localized and activated reporter gene transcription in yeast. It was highly induced in response to oxidative, salt and dehydration stresses, ABA and methyl jasmonate. Furthermore, upstream region of CsSAP09 was found to contain stress and light responsive elements. To our knowledge, this is the first report on the study of a gene family in C. sativus and may provide basic insights into the putative role of zinc finger genes. It may also serve as a valuable resource for functional characterization of these genes aimed towards unraveling their role in regulation of apocarotenoid biosynthesis.

Comprehensive transcriptome analysis of Crocus sativus for discovery and expression of genes involved in apocarotenoid biosynthesis.

BACKGROUND: Crocus sativus stigmas form rich source of apocarotenoids like crocin, picrocrocin and saffranal which besides imparting color, flavour and aroma to saffron spice also have tremendous pharmacological properties. Inspite of their importance, the biosynthetic pathway of Crocus apocarotenoids is not fully elucidated. Moreover, the mechanism of their stigma specific accumulation remains unknown. Therefore, deep transcriptome sequencing of Crocus stigma and rest of the flower tissue was done to identify the genes and transcriptional regulators involved in the biosynthesis of these compounds. RESULTS: Transcriptome of stigma and rest of the flower tissue was sequenced using Illumina Genome Analyzer IIx platform which generated 64,604,402 flower and 51,350,714 stigma reads. Sequences were assembled de novo using trinity resulting in 64,438 transcripts which were classified into 32,204 unigenes comprising of 9853 clusters and 22,351 singletons. A comprehensive functional annotation and gene ontology (GO) analysis was carried out. 58.5 % of the transcripts showed similarity to sequences present in public databases while rest could be specific to Crocus. 5789 transcripts showed similarity to transcription factors representing 76 families out of which Myb family was most abundant. Many genes involved in carotenoid/apocarotenoid pathway were identified for the first time in this study which includes zeta-carotene isomerase and desaturase, carotenoid isomerase and lycopene epsilon-cyclase. GO analysis showed that the predominant classes in biological process category include metabolic process followed by cellular process and primary metabolic process. KEGG mapping analysis indicated that pathways involved in ribosome, carbon and starch and sucrose metabolism were highly represented. Differential expression analysis indicated that key carotenoid/apocarotenoid pathway genes including phytoene synthase, phytoene desaturase and carotenoid cleavage dioxygenase 2 are enriched in stigma thereby providing molecular proof for stigma to be the site of apocarotenoid biosynthesis. CONCLUSIONS: This data would provide a rich source for understanding the carotenoid/apocarotenoid metabolism in Crocus. The database would also help in investigating many questions related to saffron biology including flower development.