Arogenate dehydratases can modulate the levels of phenylacetic acid in Arabidopsis.

Phenylacetic acid (PAA) is one type of natural auxin and widely exists in plants. Previous biochemical studies demonstrate that PAA in plants is synthesized from phenylalanine (Phe) via phenylpyruvate (PPA), but the PAA biosynthetic genes and its regulation remain unknown. In this article, we show that the AROGENATE DEHYDRATASE (ADT) family, which catalyzes the conversion of arogenate to Phe, can modulate the levels of PAA in Arabidopsis. We found that overexpression of ADT4 or ADT5 remarkably increased the amounts of PAA. Due to an increase in PAA levels, ADT4ox and ADT5ox plants can partially restore the auxin-deficient phenotypes caused by treatments with an inhibitor of the biosynthesis of indole-3-acetic acid (IAA), a main auxin in plants. In contrast, the levels of PAA were significantly reduced in adt multiple knockout mutants. Moreover, the levels of PPA are substantially increased in ADT4 or ADT5 overexpression plants but reduced in adt multiple knockout mutants, suggesting that PPA is a key intermediate of PAA biosynthesis. These results provide an evidence that members of the ADT family of Arabidopsis can modulate PAA level via the PPA-dependent pathway.