Figure 8.

Scheme Showing Contribution of DELLAs to CBF1-Mediated Growth Regulation and Freezing Tolerance.

Cold-induced or constitutive expression of CBF1 reduces bioactive GA levels (by increasing of GA2ox3 and GA2ox6 transcript abundance), thus promoting the accumulation in DELLAs by change in their protein stability. In addition, cold/CBF1 specifically increases RGL3 transcript levels. Low temperature also enhances GA2ox1 expression levels via a CBF1-independent mechanism. DELLA accumulation in turn slows plant growth. CBF1 also enhances freezing tolerance through the synergistic DELLA-dependent and COR-dependent pathways. Cold also restrains growth and promotes freezing tolerance by a DELLA-independent and CBF-independent cold response pathway.