Mortierella alpina CS10E4, an oleaginous fungal endophyte of Crocus sativus L. enhances apocarotenoid biosynthesis and stress tolerance in the host plant.

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.

Molecular phylogeny, diversity, community structure, and plant growth promoting properties of fungal endophytes associated with the corms of saffron plant: An insight into the microbiome of Crocus sativus Linn.

A total of 294 fungal endophytes were isolated from the corms of Crocus sativus at two stages of crocus life cycle collected from 14 different saffron growing sites in Jammu and Kashmir (J & K) State, India. Molecular phylogeny assigned them into 36 distinct internal transcribed spacer (ITS) genotypes which spread over 19 genera. The diversity of endophytes was higher at the dormant than at the vegetative stage. The Saffron microbiome was dominated by Phialophora mustea and Cadophora malorum, both are dark septate endophytes (DSEs). Some endophytes were found to possess antimicrobial properties that could be helpful for the host in evading the pathogens. These endophytes generally produced significant quantities of indole acetic acid (IAA) as well. However, thirteen of the endophytic taxa were found to cause corm rot in the host with different levels of severity under in vitro as well as in vivo conditions. This is the first report of community structure and biological properties of fungal endophytes associated with C. sativus, which may eventually help us to develop agro-technologies, based on plant-endophyte interactions for sustainable cultivation of saffron. The endophytes preserved ex situ, in this study, may also yield bioactive natural products for pharmacological and industrial applications.

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.

Plant-endophyte symbiosis, an ecological perspective.

Endophytism is the phenomenon of mutualistic association of a plant with a microorganism wherein the microbe lives within the tissues of the plant without causing any symptoms of disease. In addition to being a treasured biological resource, endophytes play diverse indispensable functions in nature for plant growth, development, stress tolerance, and adaptation. Our understanding of endophytism and its ecological aspects are overtly limited, and we have only recently started to appreciate its essence. Endophytes may impact plant biology through the production of diverse chemical entities including, but not limited to, plant growth hormones and by modulating the gene expression of defense and other secondary metabolic pathways of the host. Studies have shown differential recruitment of endophytes in endophytic populations of plants growing in the same locations, indicating host specificity and that endophytes evolve in a coordinated fashion with the host plants. Endophytic technology can be employed for the efficient production of agricultural and economically important plants and plant products. The rational application of endophytes to manipulate the microbiota, intimately associated with plants, can help in enhancement of production of agricultural produce, increased production of key metabolites in medicinal and aromatic plants, as well as adaption to new bio-geographic regions through tolerance to various biotic and abiotic conditions. However, the potential of endophytic biology can be judiciously harnessed only when we obtain insight into the molecular mechanism of this unique mutualistic relationship. In this paper, we present a discussion on endophytes, endophytism, their significance, and diverse functions in nature as unraveled by the latest research to understand this universal natural phenomenon.