AtDQL,an ABA Inducible Gene Regulates Seed Germination In Arabidopsis Thaliana

Seed germination, a critical stage in plant life cycle, is affected by both intrinsic factors such as plant hormones including SA (salicylic acid), ethylene, GA (gibberellins) and ABA (abscisic acid), and environmental factors including light, water, oxygen, temperature, salt stress, pests and diseases.Plant hormone ABA and GA play dominant roles in the regulation of seed germination. ABA and GA have opposite roles in seed germination, high level of ABA and low level of GA inhibit seed germination, whereas high level of GA and low of ABA promote seed germination.Several proteins such as PYLs (PYR/PYL/RCARs), PP2Cs (protein phosphatase 2C), SnRK2s (Sucrose non-fermenting 1-related protein kinase 2s) are involved in ABA signaling. When the cellural ABA level is low, PP2Cs bind and deactivate SnRK2s, thus inhibit ABA responsive gene expression. When ABA level is elevated, ABA bind to PYLs, then together to PP2Cs thus deactivate their phosphatase activaty. Consequently, SnRK2s can be activated via autophosphorylation, resulting in activation of ABA responsive genes. SnRK2s also control stomatal movement by phosphorylating SLAC1(slow anion channel 1) and KAT1(K+ channel in Arabidopsis thalianal) proteins.NCEDs (NINE-CIS-EPOXYCAROTENOID DIOXYGENASE), the key enzymes of ABA synthesis, accumulate in dry seeds of Arabidopsis thaliana, thus promoting the biosynthesis and accumucation of ABA, which in turn, induce the expression of ABI5(ABA insensitive 5), a inhibitor of seed germination. During imbibition, the expression of CYP707As(Cytochrome P450, Family 707, Subfamily A, Polypeptides) will lead to the degradation of ABA, thus inhibit the expression of ABI5. ABI1 and ABI2 are PP2C proteins that can bind and deactivate SnRK2s when ABA level is low.In an attempt to identify and characterize novel ABA response genes, we found that the expression of AtDQL(Arabidopsis thliana Dong Qiu Li) was induced by ABA. To characterize the function of AtDQL in Arabidopsis, we obtained a knockout mutant of AtDQL, atdql, generated transgenic Arabidopsis plants overexpressing AtDQL, and compared their response to ABA by using seed germination assays. We found that, when compared with Col, the mutant atldq was less sensitivity, but transgenic plant overexpressing AtDQL was more sensitivity to ABA treatment. RT-PCR analysis results showed that the expression of ABI5 was elevated in transgenic plants, but reduced in the ldq mutant. When transfected into protoplasts, AtDQL inhibited reporter gene expression. Taken together, these results indicate that AtDQL is a transcriptional represser, and it inhibits seed germination in Arabidopsis thaliana by regulating the expression of ABI5.