Editorial: Secondary metabolites and the plant adaptability to an ever-changing environment

Crocus sativus is an economically and pharmaceutically important crop. The dried stigmas of C. sativus flowers constitute saffron, the only commercial source of apocarotenoids like crocin, picrocrocin, and safranal. Some elite clones of C. sativus with higher crocin content were identified from plant populations over three years. Sequencing approach demonstrated that mutations are present in CstLycE. The C. sativus apocarotenoids are formed by cleavage of β-branch carotenoids. Cyclization of lycopene is the key branch point in carotenoid/apocarotenoid pathway. While lycopene β-cyclase converts lycopene into β-carotene, combined action of β and ε-cyclases forms α-carotene. Towards this, the mutant populations with critical mutations in CstLycE result in loss of function, and hence the metabolic flux was diverted towards β-branch. In-silico analysis and site-directed mutagenesis confirmed the critical nature of these mutations. To ascertain the role of CstLycE, transient over-expression and RNAi lines of CstLcyE in C. sativus were generated, and we observed enhanced β-branch carotenoid and apocarotenoid content in RNAi lines. The effect of CstLcyB and CstLcyE was compared, and CstLcyE RNAi lines had a more profound impact on apocarotenoid accumulation than CstLcyB over-expression lines. CstLcyE-RNAi plants also accumulated more abscisic acid and were more tolerant to abiotic stresses.