Xing Yu, Jia Wensuo, Zhang Jianhua
Department of Biology, Hong Kong Baptist University, Hong Kong, China.
Plant Mol Biol. 2009 Aug;70(6):725-36. doi: 10.1007/s11103-009-9503-0. Epub 2009 May 31.
Abscisic acid (ABA) and sugars have been well established to be crucial factors controlling seed germination of Arabidopsis. Here we demonstrate that AtMKK1 and AtMPK6 are both critical signals involved in ABA and sugar-regulated seed germination. Wild type plants depended on stratification and after-ripening for seed germination, whereas this dependence on either stratification or after-ripening was not required for mutants of mkk1 and mpk6 as well as their double mutant mkk1 mpk6. While seed germination of wild type plants was sensitively inhibited by ABA and glucose, mkk1, mpk6 and mkk1 mpk6 were all strongly resistant to ABA or glucose treatments, and in contrast, plants overexpressing MKK1 or MPK6 were super-sensitive to ABA and glucose. Glucose treatment significantly induced increases in MKK1 and MPK6 activities. These results clearly indicate that MKK1 and MPK6 are involved in the ABA and sugar signaling in the process of seed germination. Further experiments showed that glucose was capable of inducing ABA biosynthesis by up-regulating NCED3 and ABA2, and furthermore, this up-regulation of NCED3 and ABA2 was arrested in the mkk1 mpk6 double mutant, indicating that the inhibition of seed germination by glucose is potentially resulted from sugar-induced up-regulation of the ABA level.
脱落酸（ABA）和糖类已被确认为控制拟南芥种子萌发的关键因素。在此，我们证明AtMKK1和AtMPK6均为参与ABA和糖类调控种子萌发的关键信号。野生型植物种子萌发依赖于层积处理和后熟作用，而mkk1和mpk6突变体及其双突变体mkk1 mpk6则无需层积处理或后熟作用。野生型植物种子萌发受ABA和葡萄糖的敏感抑制，而mkk1、mpk6和mkk1 mpk6对ABA或葡萄糖处理均具有强抗性，相反，过表达MKK1或MPK6的植物对ABA和葡萄糖超敏感。葡萄糖处理显著诱导MKK1和MPK6活性增加。这些结果清楚地表明，MKK1和MPK6参与种子萌发过程中的ABA和糖类信号传导。进一步实验表明，葡萄糖能够通过上调NCED3和ABA2诱导ABA生物合成，此外，mkk1 mpk6双突变体中NCED3和ABA2的这种上调被阻断，这表明葡萄糖对种子萌发的抑制可能是由糖类诱导的ABA水平上调所致。
