UPS Regulates Pollen-Stigma Interactions During Arabidopsis Pollination

In higher plant, pollination is critical step in sexual reproduction, which involves manycomplex and orderly regulation mechanism. This continuous process come with pollenlanding on a stigma, followed by pollen hydration and germination, pollen tube emergenceand invasion. In recent years, great progress of molecular mechanisms and cellular bases hasbeen made in this field with many mutants and corresponding genes affect pollination processbeing identified, and mechanisms controling the key step of pollination being proposed.In our study, two Arabidopsis T-DNA insertion line of Ungerminated Pollen on Stigma(UPS) were identified. In the self-pollinated progeny of the heterozygotic mutant plants, thesegregation ratio of heterozygous to wild-type plants was about1:1, instead of the typical3:1,and no homozygous insertion was found. Reciprocal cross between wild-type plants andheterozygotic mutants revealed that mutation of this gene caused the male gametophytetransmission efficient decreased significantly. The morophology and viability of maturepollen was examined for heterozygotic mutant by using the Alexander’s staining, DAPIlabeling and pollen germination on medium. There was no significant difference of pollengrains among the wild-type and heterozygotic mutants. In heterozygous plants, the number ofseeds in mature pistils did not show any significantly difference compared with that of thewild-type. Furthermore, we found that pollen grains of heterozygous plants were easier to bewashed from the surface of the stigma than those of the wild-type. In normal environment,ups mutant pollen grains couldn’t germinate and grow on the stigma. The superstructuralanalysis revealed that the morphology of the vesicles and mitochondria in the mutant pollengrains was changed greatly. There were more small vacuoles in the mutant pollen grains, andtheir volume became larger. The inner membranes of mutant pollen grains were abnormal inmitochondrion compared with those of the wild-type. GUS staining analysis in thepUPS::GUS transgenic Arabidopsis plants and RNA in situ hybridization revealed that UPSwas expressed in pollen development process. The highest level signal was detected in pollenof stage11-flower, but the expression of UPS in mature pollen could not be detected. Ourstudy showed that UPS is important for pollen grain germination on the surface of stigma byregulating pollen and stigma interaction in Arabidopsis pollination process.