AtPrx71-mediated regulation of stem elongation, gravitropic response, and IAA accumulation in Arabidopsis.

Main conclusion: We demonstrated that Arabidopsis peroxidase AtPrx71 inhibits stem growth and gravitropism response via IAA catabolism, and speculate that other vascular plants, including poplar, may have the same functional peroxidase. Poplar peroxidase CWPO-C, which exhibits significant substrate versatility, has been suggested to participate in IAA catabolism. We previously demonstrated that AtPrx71, which shares the highest amino acid sequence identity with CWPO-C (68%) among Arabidopsis thaliana peroxidases, also possesses similar substrate versatility. Building on these findings, we hypothesized that AtPrx71 may have a function similar to that of CWPO-C in Arabidopsis. Accordingly, we analyzed the expression of AtPrx71 and examined whether AtPrx71-deficient mutant (atprx71) and AtPrx71-overexpressing transgenic Arabidopsis (35S::AtPrx71) lines exhibited altered IAA-related phenotypes. Expression analysis revealed that AtPrx71 was strongly expressed in immature organs and tissues, including the upper part of the stem, which was generally consistent with that of CWPO-C. Furthermore, the sites of high expression include many organs and tissues where auxin accumulates. With respect to stem growth, IAA accumulation and gravitropic response, the phenotypes of the atprx71 mutant and 35S::AtPrx71 lines were also consistent with the hypothesis that AtPrx71 is involved in IAA catabolism in developing stems. Finally, the amino acid sequences of CWPO-C and AtPrx71 are highly conserved among many land plants, especially dicots. Therefore, the IAA catabolic mechanisms discussed here are not restricted to poplar and Arabidopsis.