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The apocarotenoid crocetin and its glycosylated derivatives, crocins, confer the red colour to saffron. Crocetin biosynthesis in saffron is catalysed by the carotenoid cleavage dioxygenase CCD2 (AIG94929). No homologues have been identified in other plant species due to the very limited presence of crocetin and its derivatives in the plant kingdom.

Crocus sativus is the only plant species which produces apocarotenoids like crocin, picrocrocin and safranal in significant amounts. These compounds impart organoleptic properties to saffron (dried stigmas of Crocus flower) making it world’s costliest spice. Crocus apocarotenoids have tremendous medicinal properties as well. Effect of endophytes on Crocus apocarotenoid production and the molecular mechanism involved has not been reported so far. Here we studied the effect of an oleaginous fungal endophyte, Mortierella alpina CS10E4 on Crocus growth, apocarotenoid metabolism and tolerance to corm rot disease. The results demonstrated that there was a significant improvement in many morphological and physiological traits in endophyte treated Crocus plants including total biomass and size of corms, stigma biomass, number of apical sprouting buds, and number of adventitious roots. The endophyte also shifted metabolic flux towards enhanced production of apocarotenoids by modulating the expression of key pathway genes. Further, M. alpina CS10E4 enhanced tolerance to corm rot disease by releasing arachidonic acid which acts as conserved defense signal and induces jasmonic acid production in endophyte treated Crocus corms. This is first report on effect of a fungal endophyte on Crocus apocarotenoid metabolism and stress tolerance.

Summary Crocins are beneficial antioxidants and potential chemotherapeutics that give raise, together with picrocrocin, to the colour and taste of saffron, the most expensive spice, respectively. Crocins are formed from crocetin dialdehyde that is produced in Crocus sativus from zeaxanthin by the carotenoid cleavage dioxygenase 2L (CsCCD2L), while GjCCD4a from Gardenia jasminoides, another major source of crocins, converted different carotenoids, including zeaxanthin, into crocetin dialdehyde in bacterio. To establish a biotechnological platform for sustainable production of crocins, we investigated the enzymatic activity of GjCCD4a, in comparison with CsCCD2L, in citrus callus engineered by Agrobacterium‐mediated supertransformation of multi genes and in transiently transformed Nicotiana benthamiana leaves. We demonstrate that co‐expression of GjCCD4a with phytoene synthase and β‐carotene hydroxylase genes is an optimal combination for heterologous production of crocetin, crocins and picrocrocin in citrus callus. By profiling apocarotenoids and using in vitro assays, we show that GjCCD4a cleaved β‐carotene, in planta, and produced crocetin dialdehyde via C30 β‐apocarotenoid intermediate. GjCCD4a also cleaved C27 β‐apocarotenoids, providing a new route for C17‐dialdehyde biosynthesis. Callus lines overexpressing GjCCD4a contained higher number of plastoglobuli in chromoplast‐like plastids and increased contents in phytoene, C17:0 fatty acid (FA), and C18:1 cis‐9 and C22:0 FA esters. GjCCD4a showed a wider substrate specificity and higher efficiency in Nicotiana leaves, leading to the accumulation of up to 1.6 mg/g dry weight crocins. In summary, we established a system for investigating CCD enzymatic activity in planta and an efficient biotechnological platform for crocins production in green and non‐green crop tissues/organs. GjCCD4a is an efficient tool for biotechnological production of crocins in green and non‐green plant tissues. It catalyses a new route for crocetin dialdehyde formation starting with β‐carotene and proceeding via C30 β‐apo‐8′‐carotenal intermediates.

Terpene synthases (TPS) facilitate terpenoid production, influencing the flavor, color, and medicinal properties of Crocus sativus (saffron), a triploid geophyte of significant commercial importance. Despite its importance, the CsTPS gene family remains poorly characterized, limiting genetic enhancements in saffron’s agronomic features. This research performed a comprehensive genome-wide analysis of CsTPS genes using genomic, transcriptomic, and in silico approaches. BLASTP and PfamScan discovered thirty CsTPS genes, demonstrating conserved TPS domains, varied exon–intron architectures, and chromosomal clustering indicative of tandem duplications. Phylogenetic research categorized these genes into five subfamilies (TPS-a to TPS-e), with the prevalence of TPS-a suggesting a role in sesquiterpene biosynthesis. RNA-seq data (PRJNA976833, PRJNA400472) revealed tissue-specific expression, with CsTPS1 and CsTPS5 expressed in reproductive tissues and CsTPS2 in vegetative tissues. Stress-responsive genes (CsTPS1, CsTPS4) exhibited upregulation in response to cold and pathogen stress, with cis-regulatory elements (e.g., ARE, ABRE) indicating hormone control. The in-silico validation of CsTPS1, chosen for its elevated GMQE score (0.89), included primer design, ePCR, and vector optimization for expression in Arabidopsis thaliana. This study elucidates the contribution of the CsTPS family to saffron terpenoid diversity, providing a foundation for enhancing flavor, yield, and stress tolerance through genetic engineering.

Saffron crocus (Crocus sativus) is the source of the most expensive spice of the world, produced from manually harvested stigmas, thus serving as a cash crop for rural communities. However, despite its economic importance, its genome and chromosomes are poorly studied. C. sativus is a sterile triploid species harboring eight chromosome triplets, and propagated only as a clonal lineage by corms. Saffron’s evolutionary origin, parental species and allo- or autotriploidy has been a matter of discussion for almost a century. We performed a survey sequencing of the saffron genome and selected cytogenetic land-mark sequences consisting of major tandem repeats, which we used as probes in comparative multicolor fluorescent in situ hybridization (FISH). We tagged 92 chromosomal positions and resolved the chromosomal composition of saffron triplets. By comparative FISH of six Crocus species from 11 accessions, we demonstrate that C. sativus is an autotriploid hybrid derived from heterogeneous Crocus cartwrightianus cytotypes. The FISH reference karyotype of saffron is crucial for integrating genome sequencing data with chromosomes and for investigating the relationship among Crocus species. We provide an evolutionary model of the saffron emergence; the knowledge of the parental origin offers a route towards the resynthesis of C. sativus from C. cartwrightianus to broaden saffron’s gene pool.

Compartmentation is a key strategy enacted by plants for the storage of specialized metabolites. The saffron spice owes its red color to crocins, a complex mixture of apocarotenoid glycosides that accumulate in intracellular vacuoles and reach up to 10% of the spice dry weight. We developed a general approach, based on coexpression analysis, heterologous expression in yeast (Saccharomyces cerevisiae), and in vitro transportomic assays using yeast microsomes and total plant metabolite extracts, for the identification of putative vacuolar metabolite transporters, and we used it to identify Crocus sativus transporters mediating vacuolar crocin accumulation in stigmas. Three transporters, belonging to both the multidrug and toxic compound extrusion and ATP binding cassette C (ABCC) families, were coexpressed with crocins and/or with the gene encoding the first dedicated enzyme in the crocin biosynthetic pathway, CsCCD2. Two of these, belonging to the ABCC family, were able to mediate transport of several crocins when expressed in yeast microsomes. CsABCC4a was selectively expressed in C. sativus stigmas, was predominantly tonoplast localized, transported crocins in vitro in a stereospecific and cooperative way, and was able to enhance crocin accumulation when expressed in Nicotiana benthamiana leaves.

Saffron, a high‐value spice cultivated worldwide for its therapeutic and culinary uses, is a sterile triploid species, rendering conventional breeding approaches ineffective. This limitation underscores the need for molecular and biotechnological strategies for its genetic improvement. Flowering, a key determinant of saffron yield, is strongly influenced by temperature; however, the genetic regulatory networks underlying this process remain poorly understood. Our study identifies key regulators of saffron's flowering, focusing on the Florigen Activation Complex (FAC) components: FLOWERING LOCUS T (FT), bZIP transcription factor‐FD and TERMINAL FLOWER ‐1 (TFL‐1) and demonstrates their temperature‐dependent roles in floral regulation. Spatiotemporal expression analyses suggested that CsatFT3 and CsatFD2 , expressed in the floral meristem, promote floral induction, while CsatTFL1 ‐3 acts as a floral repressor. Protein interaction studies showed that CsatFT3 and CsatTFL1‐3 compete for binding to CsatFD2, and their balance modulates floral induction. Functional validation in Arabidopsis and Saffron confirmed these findings. Furthermore, we identified CsatSVP2 , an ortholog of SHORT VEGETATIVE PHASE ( SVP ), as a low temperature‐responsive repressor that directly binds the CsatFT3 promoter to inhibit its expression. Together, these findings enhance our understanding of temperature‐mediated floral induction in saffron and provide insights and lay the groundwork for genetic interventions to enhance yield under variable temperature conditions.

Saffron is the dried stigmas of Crocus sativus and is the most expensive spice in the world. Its red color is due to crocins, which are apocarotenoid glycosides that accumulate in the vacuole to a level up to 10% of the stigma dry weight. Previously, we characterized the first dedicated enzyme in the crocin biosynthetic pathway, carotenoid cleavage dioxygenase2 (CsCCD2), which cleaves zeaxanthin to yield crocetin dialdehyde. In this work, we identified six putative aldehyde dehydrogenase (ALDH) genes expressed in C. sativus stigmas. Heterologous expression in Escherichia coli showed that only one of corresponding proteins (CsALDH3I1) was able to convert crocetin dialdehyde into the crocin precursor crocetin. CsALDH3I1 carries a carboxyl-terminal hydrophobic domain, similar to that of the Neurospora crassa membrane-associated apocarotenoid dehydrogenase YLO-1. We also characterized the UDP-glycosyltransferase CsUGT74AD1, which converts crocetin to crocins 1 and 2′. In vitro assays revealed high specificity of CsALDH3I1 for crocetin dialdehyde and long-chain apocarotenals and of CsUGT74AD1 for crocetin. Following extract fractionation, CsCCD2, CsALDH3I1, and CsUGT74AD1 were found in the insoluble fraction, suggesting their association with membranes or large insoluble complexes. Analysis of protein localization in both C. sativus stigmas and following transgene expression in Nicotiana benthamiana leaves revealed that CsCCD2, CsALDH3I, and CsUGT74AD1 were localized to the plastids, the endoplasmic reticulum, and the cytoplasm, respectively, in association with cytoskeleton-like structures. Based on these findings and current literature, we propose that the endoplasmic reticulum and cytoplasm function as transit centers for metabolites whose biosynthesis starts in the plastid and are accumulated in the vacuole.

Background Phytohormones play pivotal roles in regulating floral development and secondary metabolite synthesis in saffron ( Crocus sativus L.). Results This study investigated the effects of gibberellin (GA), abscisic acid (ABA), cytokinin (CK), and strigolactone (SL) on floral differentiation, stigma quality, crocin yield, and endogenous hormonal dynamics. GA significantly accelerated floral bud differentiation and apical bud elongation during reproductive transition, increasing flower number by 23.5% compared to the control. While CK also enhanced flowering (17.6% increase), ABA and SL showed milder effects. Intriguingly, ABA treatment markedly elevated crocin content, boosting crocin 1 and 2 levels by 49.5% and 99.2%, respectively, and total crocin yield per corm by 1.7-fold-the highest among all treatments. Endogenous hormone levels were dynamically regulated, with GA and ABA treatments upregulating endogenous ABA. However, qRT–PCR analysis revealed downregulated expression of ABA biosynthesis genes ( ZEP and NCED ) under GA and ABA treatments. Conclusions These findings highlight GA as the most effective hormone for increasing flower number and ABA as the optimal choice for enhancing crocin content. This study provides actionable insights for hormone-mediated agronomic strategies to simultaneously improve saffron’s ornamental and medicinal value.

Main conclusionMutation at A126 in lycopene-β-cyclase of Crocus (CstLcyB2a) sterically hinders its binding of δ-carotene without affecting lycopene binding, thereby diverting metabolic flux towards β-carotene and apocarotenoid biosynthesis.Crocus sativus, commonly known as saffron, has emerged as an important crop for research because of its ability to synthesize unique apocarotenoids such as crocin, picrocrocin and safranal. Metabolic engineering of the carotenoid pathway can prove a beneficial strategy for enhancing the quality of saffron and making it resilient to changing climatic conditions. Here, we demonstrate that introducing a novel mutation at A126 in stigma-specific lycopene-β-cyclase of Crocus (CstLcyB2a) sterically hinders its binding of δ-carotene, but does not affect lycopene binding, thereby diverting metabolic flux towards β-carotene formation. Thus, A126L-CstLcyB2a expression in lycopene-accumulating bacterial strains resulted in enhanced production of β-carotene. Transient expression of A126L-CstLcyB2a in C. sativus stigmas enhanced biosynthesis of crocin. Its stable expression in Nicotiana tabacum enhanced β-branch carotenoids and phyto-hormones such as abscisic acid (ABA) and gibberellic acids (GA’s). N. tabacum transgenic lines showed better growth performance and photosynthetic parameters including maximum quantum efficiency (Fv/Fm) and light-saturated capacity of linear electron transport. Exogenous application of hormones and their inhibitors demonstrated that a higher ratio of GA4/ABA has positive effects on biomass of wild-type and transgenic plants. Thus, these findings provide a platform for the development of new-generation crops with improved productivity, quality and stress tolerance.