Contribution of the IAM Pathway to IAA Pool in Developing Rice Grains

Abstract

A possible role for the indole-3-acetamide (IAM) pathway in the indole-3-acetic acid (IAA) production was investigated in developing rice grains. IAM-hydrolase proposed to convert IAM to IAA primarily through the identification of IAM and IAM-hydrolase activity in some plant species. Expression profiles of the two putative rice IAM-hydrolase genes, OsAMI1&2, were compared to the previously quantified IAA level. The abrupt increase in IAA level between 4 and 7 days after anthesis (DAF) was not found to correlate with changes in the expression of OsAMI1 or OsAMID2 suggesting that the IAM pathway may not contribute significantly to IAA pool in rice grains. Production of a biological compound other than IAA may explain the high activity of OsAMI1&2 in developing rice grains. OsAMI1 that reported to be conserved across the plant kingdom showed higher expression level in most analyzed reproductive rice tissues whereas OsAMID2 showed more fluctuation in expression comparing to OsAMI1. Role of the IAM pathway in IAA production was also discussed in other plant systems and Arabidopsis seed was recommended as an ideal tissue to identify enzyme(s) convert(s) tryptophan to IAM as well as physiological effects of IAA produced via this pathway.