EXPRESSION PATTERNS OF CONVERGENTLY OVERLAPPING ARABIDOPSIS THALIANA GENE PAIRS OHP-NDP1 AND OHP2-MES14

The function of one-helix proteins (OHPs) in the thylakoid membrane remains poorly understood but may be linked to plant photosystem protection. In Arabidopsis, the 3'UTRs of the genes encoding OHP and OHP2 partially overlap with NDP1 and MES14 respectively. Antisense orientation of genes has the potential to form double-stranded transcript (dsRNA) molecules which can be processed to siRNA and trigger RNA interference (RNAi). Natural siRNAs are induced by abiotic and biotic stresses. We examined whether the expression of the OHP-NDP1 and OHP2-MES14 gene pairs is regulated in this way. Both OHP genes, but neither NDP1 nor MES14, were activated by light in etiolated seedlings, whereas cold and prolonged heat treatment elevated the OHP transcript level. Expression of OHP2 was down-regulated after 2 h of osmotic and heat stress, while salt and osmotic stress increased MES14 transcript levels. No inverse regulation of these overlapping gene pairs was observed, excluding RNAi as a regulatory mechanism in the tested conditions. The presence of alternatively polyadenylated transcripts of the studied genes raises the possibility of another regulatory mechanism of 3'UTR overlap.