The Arabidopsis thaliana adenosine 5'-phosphosulfate reductase 2 (AtAPR2) participates in flowering time and glucose response

Sugars such as sucrose or glucose function both as building materials for biosynthesis, and as signaling molecules that modulate gene expression. Compared to studies of sugar signaling in bacteria, yeast and animals, knowledge of the signaling pathways in plants is still poorly understood. Here, we investigated the effect of the disruption and overexpression of an Arabidopsis thaliana adenosine 5'-phosphosulfate reductase 2, AtAPR2, on plant responses to glucose stresses. AtAPR2 encodes an enzyme of the sulfate assimilation pathway and it is a member of a three gene family that also includes AtAPR1 and AtAPR3. Expression of AtAPR1, AtAPR2 and AtAPR3 were strongly induced by glucose treatment. Overexpression of AtAPR2 resulted in enhanced cotyledon greening and fresh weight increase when plants were treated with high glucose. By contrast, a T-DNA insertion mutant (atapr2-2) line showed delayed greening and fresh weight growth inhibition in response to glucose and also the non-metabolizable analog 2-deoxyglucose. The expression of three glucose responsive genes, Hexokinase 1 (HXK1), Phenylalanine ammonia lyase 1 (PAL1) and Pathogenesis related gene 5 (PR5), was elevated in AtAPR2-overexpressing and WT plants in response to glucose treatment, but in the atapr2-2 mutant line the transcript level for these genes decreased. Furthermore, AtAPR2-overexpressing plants displayed delayed flowering under long day condition. The data implicates AtAPR2 as a component controlling flowering time and glucose response in Arabidopsis thaliana, although the exact function of AtAPR2 is not clear.