The Role Of Type C Heterotrimeric G Protein ?-subunit In Stress Response In Cucumber

Heterotrimeric G proteins composed of a(Ga),?(G?),and ?(Gy)subunits are central signal transducers in eukaryotes.Plant Gy subunits,divided into A,B,and C types,provide proper cellular localization and functional specificity to the complex.Type C subunits,the plant-specific Gy,are potential targets for crop improvement because of their funcations in controlling major quantitative trait.Here,we studied the role of type C Gy in stress response in cucumber(Cucumis sativus L.).We demonstrated that there are five Gy-like genes in cucumber genome.We named these genes CsGGl(Cucumber Genome accession NO.:Csa2G228360),CsGG2.1(Csa2G215490),CsGG2.2(Csa3G144190),CsGG3.1(Csa2G000110),and CsGG3.2(CsalG597050).CsGG3.1 alternative splicing produces two protein variants(CsGG3.1-1 and CsGG3.1-2).The six cucumber G?homologs were divided into two classes:CsGGl,CsGG2.1 and CsGG2.2 belonged to the previously described type A,while CsGG3.1-1,CsGG3.1-2 and CsGG3.2 belonged to type C.Further study showed that the mRNA levels of CsGG3.1-l and CsGG3.1-2 were upregulated by Sphaerotheca fuliginea and salt stress,respectively.And CsGG3.2 was involved in the regulation of the CBF regulon and plant tolerance to cold stresses.We showed that CsGG3.2 transcript abundance was positively induced by cold treatments.Transgenic cucumber plants(T1)constitutively overexpressing CsGG3.2 exhibits tolerance to chilling conditions and increased expression of CBF genes and their regulon genes.Antioxidative enzymes,i.e.,superoxide dismutase(SOD),catalase(CAT),peroxidase(POD),and glutathione reductase(GR)activities increased in cold-stressed transgenic plants.The reactive oxygen species(ROS),Oxygen free radical(OFR)and H2O2,production,as well as membrane lipid peroxidation(MDA)production decreased in transgenic plants,suggesting a better antioxidant system to cope the oxidative-damages caused by cold stress.