Analysis ofArabidopsisglucose insensitive mutants,gin5andgin6, reveals a central role of the plant hormone ABA in the regulation of plant vegetative development by sugar

Sugars have signaling roles in a wide variety of developmental processes in plants. To elucidate the regulatory components that constitute the glucose signaling network governing plant growth and development, we have isolated and characterized twoArabidopsisglucose insensitive mutants,gin5andgin6, based on a glucose-induced developmental arrest during early seedling morphogenesis. The T-DNA-taggedgin6mutant abrogates the glucose-induced expression of a putative transcription factor, ABI4, previously shown to be involved in seed-specific abscisic acid (ABA) responses. Thus, ABI4 might be a regulator involved in both glucose- and seed-specific ABA signaling. The characterization of thegin5mutant, on the other hand, reveals that glucose-specific accumulation of ABA is essential for hexokinase-mediated glucose responses. Consistent with this result, we show that three ABA-deficient mutants (aba1-1, aba2-1, andaba3-2) are also glucose insensitive. Exogenous ABA can restore normal glucose responses ingin5andabamutants but not ingin6plants. Surprisingly, onlyabi4andabi5-1but not other ABA-insensitive signaling mutants (abi1-1, abi2-1, andabi3-1) exhibit glucose insensitivity, indicating the involvement of a distinct ABA signaling pathway in glucose responses. These results provide the first direct evidence to support a novel and central role of ABA in plant glucose responses mediated through glucose regulation of both ABA levels by GIN5 and ABA signaling by GIN6/ABI4.