Plant acclimatory responses to
phosphate (Pi)
starvation stress include the accumulation of
carbohydrates, namely
sugar and
starch. However, whether altered endogenous
carbohydrate profile could in turn affect plant Pi
starvation responses remains widely unexplored. Here, two genes encoding the large and small subunits of an
ADP-glucose pyrophosphorylase (AGP) in rice (Oryza sativa), AGP Large Subunit 1 (AGPL1) and AGP Small Subunit 1 (AGPS1), were functionally characterized with regard to maintenance of
phosphorus (P) homeostasis and regulation of Pi
starvation signaling. AGPL1 and AGPS1 were both positively responsive to
nitrogen (N) or Pi deprivation, and expressed in almost all the tissues except in the meristem and mature zones of root. AGPL1 and AGPS1 physically interacted in chloroplast, and catalyzed the rate-limiting step of
starch biosynthesis. Low-N- (LN) and low-Pi (LP)-triggered
starch accumulation in leaves was impaired in agpl1, agps1 and apgl1 agps1 mutants compared with the wild-type plants. By contrast, mutation of AGPL1 and/or AGPS1 led to an increase in the content of the major
sugar,
sucrose, in leaf sheath and root under control and LN conditions. Moreover, the Pi accumulation was enhanced in the mutants under control and LN conditions, but not LP conditions. Notably, the LN-induced suppression of Pi accumulation was compromised attributed to the mutation of AGPL1 and/or AGPS1. Furthermore, the increased Pi accumulation was accompanied by the specific suppression of OsSPX2 and activation of several Pi transporter genes. These results indicate that a balanced level of
carbohydrates is vital for maintaining plant P homeostasis.