PT  - JOURNAL ARTICLE
AU  - Federica Brunoni
AU  - Silvio Collani
AU  - Rubén Casanova-Saéz
AU  - Jan Šimura
AU  - Michal Karady
AU  - Markus Schmid
AU  - Karin Ljung
AU  - Catherine Bellini
TI  - Conifers exhibit a characteristic inactivation of auxin to maintain tissue homeostasis
AID  - 10.1101/789420
DP  - 2019 Jan 01
TA  - bioRxiv
PG  - 789420
4099  - http://biorxiv.org/content/early/2019/10/01/789420.short
4100  - http://biorxiv.org/content/early/2019/10/01/789420.full
AB  - Dynamic regulation of the levels of the natural auxin, indol-3-acetic acid (IAA), is essential to coordinate most of the physiological and developmental processes and responses to environmental changes. Oxidation of IAA is a major pathway to control auxin concentrations in Arabidopsis and, along with IAA conjugation, to respond to perturbation of IAA homeostasis. However, these regulatory mechanisms are still poorly investigated in conifers. To reduce this gap of knowledge, we investigated the different contribution of the IAA inactivation pathways in conifers.Mass spectrometry-based quantification of IAA metabolites under steady state conditions and after perturbation was investigated to evaluate IAA homeostasis in conifers. Putative Picea abies GH3 genes (PaGH3) were identified by a comprehensive phylogenetic analysis including Arabidopsis and basal land plants. Auxin-inducible PaGH3 genes were identified by expression analysis and their IAA-conjugating activity was explored.Compared to Arabidopsis, oxidative and conjugative pathways differentially contribute to reduce IAA levels in conifers. We demonstrated that the oxidation pathway plays a marginal role in controlling IAA homeostasis in spruce. On the other hand, an excess of IAA rapidly activates GH3-mediated irreversible conjugation pathways.Taken together, these data indicate that a diversification of IAA inactivation mechanisms evolved specifically in conifers.