Practice question

Elicitors boost secondary metabolite production by mimicking biotic attack triggering plant innate defense signaling and activation of defence related enzymes. Biotic elicitors include fungal cell wall fragments chitin chitosan glucans yeast extract bacterial flagellin; abiotic include jasmonic acid methyl jasmonate salicylic acid heavy metals copper cadmium UV-C ozone. Perception by pattern recognition receptors triggers calcium influx cyclic nucleotide gated channels, production of reactive oxygen species via NADPH oxidase RBOH, activation of mitogen activated protein kinase cascades MPK3 MPK6 leading to jasmonate isoleucine synthesis. Jasmonate signals transcription factors MYB WRKY ORCA that bind promoters of phenylpropanoid pathway enzyme phenylalanine ammonia lyase PAL cinnamate 4 hydroxylase chalcone synthase CHS, and terpenoid pathway HMGR terpene synthase. Resulting phytoalexins alkaloids paclitaxel vincristine flavonoids accumulate up to tenfold. Commercial process employs two stage culture: biomass accumulation stage low elicitor high auxin, then production stage elicitor addition at late exponential phase to redirect carbon flux from primary to secondary metabolism without severe growth inhibition enabling industrial bioreactor harvesting.