Amino acid conjugation of oxIAA is a secondary metabolic regulation involved in auxin homeostasis

Application of Long-Chained Auxin Conjugates Influenced Auxin Metabolism and Transcriptome Response in Brassica rapa L. ssp. pekinensis

“…This is in contrast to the results observed with exogenous IAA treatments [ 35 , 36 ], where “feeding” A. thaliana with high concentrations of IAA (above 5 µmol L −1 ) increased IAA conjugation to Asp and Glu and further oxidation of IAA-Asp to oxIAA-Asp and OH-IAA-Asp, while treatments with lower concentrations of exogenous IAA (below 0.5 µmol L −1 ) mainly increased oxIAA. Recent research has shed new light on auxin inactivation as a part of auxin homeostasis and has shown that the process of auxin inactivation is more complex, comprising the complete GH3-ILR1-DAO enzyme pathway [ 30 , 31 ]. It has been shown that IAA is first converted to IAA-amino acid conjugates (IAA-Asp and IAA-Glu) by GH3 enzymes, and then IAA-Asp and IAA-Glu can be converted back to IAA by ILR1/ILL amidohydrolases or irreversibly oxidized to oxIAA-Asp and oxIAA-Glu by DAO1 dioxygenase.…”

“…oxIAA-Asp and oxIAA-Glu can subsequently be hydrolyzed by ILR1 to release inactive oxIAA. Furthermore, based on comparative feeding experiments on A. thaliana , Picea abies and Physcomitrium patens , Brunoni et al [ 31 ] reported that the pathway of auxin inactivation is species-specific. At the moment, we were not able to measure all intermediates of the auxin inactivation pathway.…”

“…At least for Arabidopsis, the substrates for most of the different GH3 proteins have been elucidated. The GH3.3 as well as the other GH3 proteins 3.1 to 3.6 are involved in the conjugation of IAA and oxIAA to amino acids [ 31 , 44 ]. The GH3.12 protein is involved in the biosynthesis of salicylic acid [ 45 ] and its expression was not detected in our system ( Figure 6 B).…”

“…GH3.2 (YDK1) was significantly induced by the treatments applied here ( Figure 5 ), and some GH3 genes showed a tendency to induce their expression after treatments with auxin conjugates ( Figure 6 B,) although this had no effect on the level of identified auxin amino acid conjugates (IAA-Asp and IAA-Glu) in B. rapa seedlings after the treatments. Based on the data of Brunoni et al [ 31 ], the group II GH3 enzymes, AtGH3.1, AtGH3.2, AtGH3.3, AtGH3.5, AtGH3.6 and AtGH3.17, showed activity with oxIAA; AtGH3.2, AtGH3.3 and AtGH3.5 conjugated oxIAA preferentially with Asp, whereas AtGH3.1 and AtGH3.6 conjugated oxIAA exclusively with Asp and AtGH3.17 with Glu. Furthermore, AtGH3.2 conjugates oxIAA with Leu and Phe.…”

Synthetic and analytical routes to the L-amino acid conjugates of cis-OPDA and their identification and quantification in plants

“…Modification of chemical structures alters their biological activity and determines their degradation, storage, or activation (Westfall et al, 2013). The amino acid conjugation of acidic phytohormones mediated by the GRETCHEN HAGEN 3 (GH3) acyl acid-amido synthetases is a conserved mechanism involved in the dynamic regulation of the cellular levels of JAs, auxins, and benzoates (Brunoni et al, 2020;Brunoni et al, 2023;Staswick et al, 2005;Staswick et al, 2002;Westfall et al, 2016). Amino acid conjugation of auxins attenuates their bioactivity.…”