ADG2-1 REPRESENTS A MISSENSE MUTATION IN THE ADPG PYROPHOSPHORYLASE LARGE SUBUNIT GENE OF ARABIDOPSIS-THALIANA

Arabidopsis mutants affecting ADPG pyrophosphorylase (ADGase) activity can be divided into two complementation groups, adg1 and adg2. Previo us biochemical studies of adg2-1 mutant indicated that mutant plants d o not accumulate ADGase large subunit protein and that ADGase small su bunits assemble as homotetramers. This suggested that the ADG2 gene ma y encode the large subunit of ADGase. In this paper, it is shown that adg2-1 mutant plants accumulate near wild-type levels of transcripts e ncoding both the large and small subunits of ADGase. However, by RFLP analysis and complementation of adg2-1 with the ADGase large subunit g ene, we show that the adg2-1 mutant does represent a mutation of the A DGase large subunit gene. Sequence analysis of the adg2-1 allele revea led a missense mutation. The results therefore suggest either that the missense mutation affects the stability of the ADGase large subunit p rotein or that it prevents assembly of the large subunit into holoenzy me.