Fitness cost of impaired jasmonate catabolism under plant competition in Arabidopsis thaliana

LICHY MICAELA Z; CARGNEL MIRIAM D; BALLARÉ CARLOS L

Simposio; Frontiers in Bioscience 4; 2023

When plants detect pathogens or herbivores, defense responses are induced and plant growth is often halted. In contrast, when plants detect competitors, growth ispromoted and defense responses are attenuated. Important plant hormones that modulate these antagonistic responses are the jasmonates (JAs), which can activate chemical defense and are also potent growth inhibitors. The sulfotransferase 2a (ST2a) is an enzyme that catalyzes the sulfation of 12-hydroxy jasmonic acid to form the inactive 12-hydroxy jasmonic acid sulfate. The inactivation of JAs by ST2a pathway has been recently reported as a novel defense attenuation mechanism in response to competition signals (low Red/Far-Red ratios) under controlled-environment conditions.We assessed the fitness costs of lacking the ST2a inactivation pathway in plants that growunder competition with real neighbors. We carried a competition experiment in thegreenhouse using two genotypes of Arabidopsis, a ST2a null mutant (st2a-1) and the Columbia wild type (Col-0), grown in monocultures or mixed stands.During canopy development, st2a-1 mutants were impaired in their ability to capture directsunlight, compared to their Col-0 competitors. This disadvantage correlated with an increased flux of JAs through the aminoacid conjugation pathway that leads to the synthesis of bioactive products (JA-Ile), and an increased expression of JA-Ile marker genes and defense metabolites in st2a-1 compared to Col-0. At harvest, we found that the reproductive output of st2a-1 plants was greatly compromised in mixed stands. However, in high densitymonocultures, the final fruit production of st2a-1 mutants did not differ from that of Col-0canopies.We conclude that attenuation of JA signaling through ST2a is an importantdeterminant of competitive ability and it is required to maximize individual fitness. At thepopulation level, however, the lack of the ST2a gene does not result in reduced fruit yield.