Localized auxin biosynthesis and postembryonic root development in Arabidopsis

摘要

Auxin is a phytohormone essential for plant development. Due to the high redundancy in auxin biosynthesis, the role of auxin biosynthesis in embryogenesis and seedling development, vascular and flower development, shade avoidance and ethylene responsewere revealed only recently. We previously reported that a vitamin Bg biosynthesis mutant pdxl exhibits a short-root phenotype with reduced meristematic zone and short mature cells. By reciprocal grafting, we now have found that the pdxl short root is caused by a root locally generated signal. The mutant root tips are defective in callus induction and have reduced DR5::GUS activity, but maintain relatively normal auxin response. Genetic analysis indicates that pdxl mutant could suppress the root hair and root growth phenotypes of the auxin overproduction mutant yucca on medium supplemented with tryptophan (Trp), suggesting that the conversion from Trp to auxin is impaired in pdxl roots. Here we present data showing that pdxl mutant is more tolerant to5-methyl anthranilate, an analogue of the Trp biosynthetic intermediate anthranilate, demonstrating that pdx1 is also defective in the conversion from anthranilate to auxin precursor tryptophan. Our data suggest that locally synthesized auxin may play an important role in the postembryonic root growth.