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Intracellular membrane fusion is effected by SNARE proteins that reside on adjacent membranes and form bridging trans-SNARE complexes. Qa-SNARE members of the Arabidopsis SYP1 family are involved in membrane fusion at the plasma membrane or during cell plate formation. Three SYP1 family members have been classified as pollen-specific as inferred from gene expression profiling studies, and two of them, SYP124 and SYP125, are confined to angiosperms. The SYP124 gene appears genetically unstable, whereas its sister gene SYP125 shows essentially no variation among Arabidopsis accessions. The third pollen-specific member SYP131 is sister to SYP132, which appears evolutionarily conserved in the plant lineage. Although evolutionarily diverse, the three SYP1 proteins are functionally overlapping in that only the triple mutant syp124 syp125 syp131 shows a specific and severe male gametophytic defect. While pollen development and germination appear normal, pollen tube growth is arrested during passage through the style. Our results suggest that angiosperm pollen tubes employ a combination of ancient and modern Qa-SNARE proteins to sustain their growth-promoting membrane dynamics during the reproductive process., (© 2017 The Authors The Plant Journal © 2017 John Wiley & Sons Ltd.)

Membrane traffic contributes to plant growth and development. However, the functional significance of SNARE proteins involved in membrane fusion of the early secretory pathway has not been explored with respect to plant development. Here we analyze the Arabidopsis v-SNARE SEC22. Loss of SEC22 function impairs gametophyte development, as indicated by reciprocal crosses between wild-type plants and plants heterozygous for T-DNA insertions in the SEC22 gene. sec22 mutant pollen becomes abnormal during the bicellular stage, eventually giving rise to degenerated pollen grains. Most mutant embryo sacs fail to support embryogenesis and display unfused polar nuclei in their central cell. Immunolocalization by both light and electron microscopy revealed an association of mutant-complementing Myc-tagged SEC22 with the central and peripheral endoplasmic reticulum (ER). Ultrastructural analysis of developing sec22 mutant pollen demonstrated Golgi fragmentation and consumption. As a consequence, the plasma membrane-targeted syntaxin SYP124 was retained in the ER. Our results suggest that SEC22 plays an essential role in early secretory traffic between the ER and the Golgi., (© 2011 The Authors. The Plant Journal © 2011 Blackwell Publishing Ltd.)