Expression of GEX1 Orthologs of and Rescued the Nuclear Fusion Defect of the Arabidopsis GEX1 Mutant.

Nuclear fusion is required for the sexual reproduction of various organisms, including angiosperms. During the life cycle of angiosperms, nuclear fusion occurs three times: once during female gametogenesis, when the two polar nuclei fuse in the central cell, and twice during double fertilization. Nuclear fusion in plant reproduction is achieved by sequential nuclear fusion events: outer and inner nuclear membrane fusion. gamete expressed 1 (GEX1) is a nuclear membrane protein of gametes that is required for nuclear fusion during reproduction. Although orthologs of GEX1 have been identified in various land plants, sequence identities are not high, even between angiosperm GEX1 orthologs; the sequence identity between GEX1 and GEX1 ortholog is lower than 50%. Here, we found that the expression of GEX1 orthologs of , as well as of from the promoter, rescued the polar nuclear fusion defect of the mutant. We also found that the expression of these GEX1 orthologs rescued the lethality of the homozygous mutant, which is proposed to be caused by the sperm nuclear fusion defects upon fertilization. Our results indicate a functional conservation between and GEX1 orthologs, despite their relatively low sequence identities.