The Role of Gibberellin in the CBF1-Mediated Stress-Response Pathway

Constitutive expression of C-repeat/dehydration-responsive element binding factor genes confers drought, salt, and freezing tolerance in transgenic plants but causes dwarfism under normal growth conditions. Evidence has emerged that gibberellin (GA) plays a major role in these growth-regulatory mechanisms. However, the role and benefit of reducing the active GA level in abiotic stress responses are largely unknown. Using microarray analysis, we identified a subgroup of GA-regulated genes by comparing the transcriptome of GA over-accumulation and deficiency, CBF1 constitutive expression, and wild-type tobacco plants (Nicotiana tabacum). The results revealed that the geranylgeranyl diphosphate synthase is a regulatory site integrating environmental cues and is endogenous in the regulation of GA level and subsequent plant growth. Low levels of GA promoted the accumulation and gene activation of osmotic adjustment-related substances and enhanced the water-retention capability of leaves. We found that GA was associated with SA/JA balance in the CBF1-mediated stress response, but inhibition of SA signaling is the principal regulator in this pathway. These results demonstrate that, in addition to regulating growth, GA has a much more complex role, and SA may be another important player in the CBF1-mediated stress-response pathway.