The Role Of Heterotrimeric G Protein In Pollen Germination And Leaf Development Of Arabidopsis (Appendix: The Effect Of Extracellular CaM On Gene Expression)

Our previous pharmacological analysis suggested the involvement of heterotrimeric Ga subunit in transmembrane signal transduction of extracellular calmodulin in pollen germination and tube growth. In the present study, we further tested the action of heterotrimeric G proteins in Arabidopsis pollen germination and tube growth by using several G protein null mutants and overexpression strains.The results were as followed: pollen germination and tube growth were decreased in Ga mutant, and increased in Ga overexpression strains as compared to wild type, while pollen germination and tube growth were not affected in Gp mutant. It was also found that the average number of germinated pollen grains on each stigma of Ga mutant was less than that of wild type, while in Ga overexpression strains the average number was more than that of control (wild type and empty vector control). There were little difference between Gp mutant and control in the number of germinated pollen grain in vivo.The concentration of cytosolic free calcium in both pollen grain and pollen tube was lower in Ga mutant and higher in Ga overexpression strains than that of control. The level of cytosolic free calcium in Gp mutants is not different.Adding exogenous purified CaM to the cultural medium increased the pollen germination, tube growth, and cytosolic free calcium concertration in both wild type and Ga mutant. However, the former was more sensitive to exogenous CaM than the latter.All of above main results suggested that Ga was involved in pollen germination and tube grown by regulating cytosilic free calcium level, whereas Gp was not, and extracellular CaM might regulate pollen germination and tube growth through Ga.The heterotrimeric G proteins had participated in several other development processes in Arabidopsis. Here we found G proteins also function in leaf, silique development and the yield of pollen microspore. We observed several traits or characters in the offsprings of gpal, agblnull mutation and GPA1 overexpression lines and found that the width of mutants' lamina is larger than that of the wild type, whereas the lamina length, petiole length and rosette diameter is smaller than the wild type, the Ga overexpression lines is different from the mutants; the silique length and the pedicel length is larger in mutants than that of wild type, and slightly smaller in overexpression lines than the control; the morphometric character in silique tip is different in gpal from agbl mutants; the yield of pollen microspore is larger in null mutants than wild type whereas smaller in overexpression lines. The finding that GPA1 and AGB1 are involved in the control of several organ shape suggests that heterotrimeric G protein signaling is a versatile developmental regulator in Arabidopsis and the a, p subunit of G protein maybe operate in different manner in the regulation of Arabidopsis development from our experiment.