The impact on nitrogen-efficient phenotypes when aspartate aminotransferase is expressed tissue-specifically in Brassica napus

Background

Aspartate aminotransferase (AAT) catalyzes a reversible transamination reaction, producing aspartate and 2-oxoglutarate from glutamate and oxaloacetate, in various cellular plant compartments. Previous work in our lab had shown that a similar aminotransferase enzyme, alanine aminotransferase (AlaAT), produced nitrogen use efficient (NUE) phenotypes when over-expressed in canola (Brassica napus) under the salt-stress inducible promoter, btg-26. Given the similarities between these two enzymes and their roles in plant metabolism, it was hypothesized that over-expression of AAT could also produce an NUE phenotype in canola.

Results

Transgenic Brassica napus lines over-expressing AAT from Medicago sativa were produced and analyzed for NUE phenotypes under both high and low nitrogen conditions. While several lines showed promising increases in biomass under the various fertilizer regimes, these alterations could not be reliably replicated and increases in expression of the transgene detected via RT-PCR did not translate into significant increases in AAT activity in plant tissues.

Conclusions

Transgenic Brassica napus lines over-expressing AAT do not display NUE phenotypes similar to those plants over-expressing AlaAT. Although this work produced a negative result, it is important to compare the NUE phenotype produced by over-expression of AlaAT and AAT, and differences in metabolism between AAT vs AlaAT over-expressing lines which may be used to deduce changes in plant N metabolism important for NUE in cereal crops.