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

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 derepression
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.