Abstract 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 polyadenylat-ed transcripts of the studied genes raises the possibility of another regulatory mechanism of 3'UTR overlap.

Abstract Mechanical damage to scales of Hippeastrum × hybr. bulbs leads to the formation of phytoalexin-like compounds which redden the wounded tissue. The reaction is accompanied by an increase in methyl jasmonate (JA-Me). Applying 2-(4-isobutylphenyl) propionic acid, a jasmonate biosynthesis inhibitor, decreases the level of endogenous jasmonates and decreases the plant's ability to produce the red pigment. Experimental results indicate that jasmonates are involved in the defense response to wounding in Hippeastrum, which is manifested in the formation of red pigment, a compound of chalcones and flavans with phytoalexin-like properties.