Salicylic acid and methyljasmonate restore the transcription of caffeine biosynthetic N-methyltransferases from a transcription inhibition noticed during late endosperm maturation in coffee

• SA/MeJ stress stimuli de-represses developmental repression of NMT genes.
• Extant/basal DXMTs and not transcript de-repression cause an increase in caffeine.
• High SA may lead to post-transcriptional check in the extent of caffeine accumulation.
• Development and stress factors may interact during caffeine content determination.

Transcripts of the three N-methyltransferase (NMT) genes involved in the core caffeine biosynthesis of coffee are repressed during the early stages of endosperm maturation, coincident with the onset of dry weight accumulation and seed desiccation. Previously, we noticed that the exogenous application of salicylic acid (SA) and methyljasmonate (MeJ) to Coffea canephora var. robusta cv. S-274 overexpresses transcripts of the three NMTs in young leaves. Thus, transcriptional regulation of caffeine biosynthetic genes may play a vital role in caffeine accumulation. We carried out this study to find if salicylic acid (SA) (50 μM and 500 μM concentrations) and MeJ treatment of the maturing fruits is capable of restoring the transcription activity of NMT genes. MeJ leads to overexpression of the first two NMTs (XMTs and MXMTs) whereas the effect of SA appeared to be concentration-dependent. Though SA (500 μM) de-repressed all three NMTs, SA (50 μM) restored transcription of only the second NMT. Neither SA (50 μM) nor MeJ could restore transcription of the third and final NMT (DXMTs) of the pathway. Biochemical estimation of methylxanthines indicates a slight but significant increase in theobromine content (11.8% increase) in endosperms treated with 50 μM SA. Caffeine showed a statistically significant increase in both MeJ (14.4% increase) and SA (50 μM) (14.8% increase) treatments. Since de-repression in DXMTs (caffeine synthase) was not observed, theobromine to caffeine conversion in MeJ and SA (50 μM) treated fruits is probably catalyzed by the basal or the extant DXMT gene product. Caffeine levels remained constant in SA (500 μM) treatments indicating a possible post-transcriptional regulation. These results are indicative of cross talk between the cascades induced by SA and MeJ and the maturation-induced regulation of caffeine accumulation and may be helpful in studying the interaction between these pathways.