INVESTIGATION OF THE POTENTIAL ROLE OF ALDEHYDE OXIDASE IN INDOLE-3-ACETIC ACID SYNTHESIS OF DEVELOPING RICE GRAINS

Aldehyde oxidase (AO) was proposed to convert indole-3-acetaldehyde (IAAld) to indole-3-acetic acid (IAA) primarily through the identification of endogenous IAAld and the efficient conversion of IAAld to IAA via AO. Involvement of AO in the production of IAA has been investigated in developing rice grains (OsAO). Analysis of phylogenetic tree, RT-PCR as well as online microarray data confirmed that rice inherited two groups of AO; OsAO1-3, and OsAO4. OsAO1-3 were found to be very similar and may arise as a result of recent duplication. RT-PCR analysis confirmed that OsAO1 but not OsAO2 or OsAO3 was expressed in the developing rice grains at 1, 7, and 21 days after flowering (DAF). Change in the expression of OsAO1 was found to be parallel to the previously reported abrupt change in IAA level between 4-7 DAF suggesting that OsAO1 may have a role in IAA synthesis at least in this system. The top 300 genes list created by co-expression analysis contained OsYUCCA9 and OsYUCCA11 which reported to have a significant role in IAA synthesis through the indole-3-pyruvic acid (IPA) pathway. Lack of correlation between the two transcripts of OsAO4 and changes in IAA level may give a negative indication for the involvement of OsAO4 in de novo IAA synthesis.