Deciphering the role of stress elicitors on the differential modulation of chalcone synthase gene and subsequent production of secondary metabolites in micropropagated Coelogyne ovalis Lindl., a therapeutically important medicinal orchid

Abstract

• Stress elicitors treatment (salicylic acid, methyl jasmonate, abscisic acid, chitosan and yeast extract) upregulated the expression of chalcone synthase gene in Coelogyne ovalis . • Salicylic acid treatment resulted in the highest CoCHS expression, secondary metabolites (total phenolic, total flavonoids, total anthocyanins) accumulation and antioxidant activity. • The expression of chalcone synthase is positively correlated with accumulation of secondary metabolites which implying the possible role of stress in the enhancement of secondary metabolites of interest in the orchid, Coelogyne ovalis . Coelogyne ovalis Lindl. is one of the important medicinal orchid, has been used in traditional medicines for the treatment of various human aliments. The therapetical uses of this orchid may be attributed to the presence of various secondary metabolites ultimately produced via the phenylpropanoid pathway. Amongst the various genes involved in phenylpropanoid pathway, chalcone synthase (CHS) deserves a special mention as it plays a pivotal role in the synthesis of secondary metabolites. In the present research, an attempt has been made to modulate the expressions of CHS transcript and subsequent enhancement in the production of secondary metabolites (phenolics, flavonoids and anthocyanins) and antioxidant activity by the application of biotic (chitosan and yeast extracts) and abiotic (salicylic acid, methyl jasmonate and abscisic acid) stresses to the in vitro -raised plantlets. Amongst the various stress factors taken into consideration, salicylic acid-treated leaves showed the highest tissue-specific expression pattern (13.53-fold at 50 μM), followed by methyl jasmonate (10.80-fold at 100 μM), chitosan (9.04-fold at 100 μM) as compared to control plantlets. The correlation between CHS expression and the presence of secondary metabolites was also studied to find out a suitable condition which would result in higher accumulation of secondary metabolites. Further, elicitations with best three stresses (namely salicylic acid, methyl jasmonate and chitosan) significantly modulated the accumulation of secondary metabolites. Deviations were also detected in terms of phytochemical contents; the salicylic acid-treated leaf tissues showed the highest contents of flavonoids (34.18 mg QE/gm DW) and anthocyanins (24.08 mg / gm FW) whereas phenolic contents were recorded to be highest in pseudobulbs (44.61 mg GAE/ gm DW). The plantlets treated with salicylic acid resulted in enhanced production of secondary metabolites and significantly higher antioxidant activity (DPPH and metal chelating). The present result suggests that stress stimulates CoCHS expression and secondary metabolites production in the treated tissues of C. ovalis .