α-aminoisobutyric acid mimics the effect of 1-aminocyclopropane-1-carboxylic acid to promote sexual reproduction in the marine red alga Pyropia yezoensis (Rhodophyta)

1-aminocyclopropane-1-carboxylic acid (ACC), a precursor for ethylene, stimulates the switch from a vegetative to a sexual reproductive phase in the marine red alga Pyropia species. This study explored the effects of ethylene biosynthesis inhibitors on the sexual reproduction of gametophytes of the red alga Pyropia yezoensis to gain a functional understanding of the role of ACC as a plant hormone in red algae. Here we show that two inhibitors of ACC synthesis in higher plants, 2-aminoethoxyvinyl glycine (AVG) and aminooxyacetic acid (AOA), had no effect on the growth and gametogenesis of P. yezoensis. In contrast, exogenous application of alpha-aminoisobutyric acid (AIB), a structural analog of ACC that blocks the conversion of ACC to ethylene in higher plants, induced the formation of spermatangia and carpospores in a similar manner as ACC, without endogenous ACC accumulation. The treatment of AIB failed to inhibit ethylene production in the gametophytes. The present results suggest that AIB mimics the effect of ACC to induce the sexual reproduction and support our previous study that ACC has a role in the regulation of the sexual reproduction independent from ethylene.