Sialyltransferases （SlaTs） exist widely in vertebrates and play important roles in a variety of biological processes. In plants, several genes have also been identified to encode the proteins that share homology with the vertebrate SlaTs. However, very little is known about their functions in plants. Here we report the identification and characterization of a novel Arabidopsis gene, MALE GAMETOPHYTE DEFECTIVE 2 （MGP2） that encodes a sialyltransferase-like protein. MGP2 was expressed in all tissues including pollen grains and pollen tubes. The MGP2 protein was targeted to Golgi apparatus. Knockout of MGP2 significantly inhibited the pollen germination and retarded pollen tube growth in vitro and in vivo, but did not affect female gametophytic functions. These results suggest that the sialyltransferase-like protein MGP2 is important for normal pollen germination and pollen tube growth, giving a novel insight into the biological roles of the sialyltransferase.like proteins in plants.
Yi Deng Wei Wang Wen-Qing Li Chuan Xia Hong-Ze Liao Xue-Qin Zhang De Ye
In flowering plants, the exine components are derived from tapetum. Despite its importance to sexual plant reproduction, little is known about the translocation of exine materials from tapetum to developing microspores. Here we report functional characterization of the arabidopsis WBC27 gene. WBC27 encodes an adenosine tri-phosphate binding cassette （ABC） transporter and is expressed preferentially in tapetum. Mutation of WBC27 disrupted the exine formation. The wbc27 mutant microspores began to degenerate once released from tetrads and most of the microspores collapsed at the uninucleate stage. Only a small number of wbc27-1 microspores could develop into tricellular pollen grains. These survival pollen grains lacked exine and germinated in the anther before anthesis. All of these results suggest that the ABC transporter, WBC27 plays important roles in the formation of arabidopsis exine, possibly by translocation of lipidic precursors of sporopollenin from tapetum to developing microspores.
Xiao-Ying DouKe-Zhen YangYi ZhangWei WangXiao-Lei LiuLi-Qun ChenXue-Qin ZhangDe Ye
The female gametophyte is crucial for sexual reproduction of higher plants, yet little is known about the molecular mechanisms underlying its development. Here, we report that Arabidopsis thaliana NOP10 （AtNOP10） is required for female gametophyte formation. AtNOP10 was expressed predominantly in the seedling and reproductive tissues, including anthers, pollen grains, and ovules. Mutations in AtNOP10 interrupted mitosis of the functional megaspore during early development and prevented polar nuclear fusion in the embryo sacs. AtNOP10 shares a high level of amino acid sequence similarity with Saccharornycescerevisiae （yeast） NOPIo （ScNOP1o）, an important compo- nent of the H/ACA small nucleolar ribonucleoprotein particles （H/ACA snoRNPs） implicated in 18S rRNA synthe- sis and rRNA pseudouridylation. Heterologous expression of ScNOP10 complemented the mutant phenotype of Atnop10. Thus, AtNOPIo influences functional megaspore mitosis and polar nuclear fusion during gametophyte formation in Arabidopsis.
In flowering plants, male gametes are delivered to female gametophytes by pollen tubes. Although it is important for sexual plant reproduction, little is known about the genetic mechanism that controls pollen germination and pollen tube growth. Here we report the identification and characterization of two novel mutants, gnom-like 2-1 （gnl2-1） and gn12-2 in Arabidopsis thaliana, in which the pollen grains failed to germinate in vitro and in vivo. GNL2 encodes a protein homologous to the adenosine diphosphate-ribosylation factor-guanine nucleotide exchange factors, GNOM and GNL1 that are involved in endosomal recycling and endoplasmic reticulum-Golgi vesicular trafficking. It was prolifically expressed in pollen grains and pollen tubes. The results of the present study suggest that GNL2 plays an important role in pollen germination.
Dong-Jie JiaXi CaoWei WangXiao-Yun TanXue-Qin ZhangLi-Qun ChenDe Ye
