From our NSF Plant Genome project (see previous research topics) we identified several candidates that are sperm- or egg-expressed. We are particularly interested in proteins that are on the gamete surface, or that are secreted. For example, we showed that GEX3, a plasma membrane-localized protein, is expressed in both the sperm and egg and plays a role in pollen tube guidance (Alandete-Saez, Ron and McCormick, 2008). Functional analyses of other candidates are on-going. We provided Arabidopsis lines with GFP-tagged sperm cells to Jose Feijo's lab, and they used them to determine the transcriptome of sperm cells (Borges et al., 2008). This was important, since we had only sequenced ~5000 maize sperm ESTs and therefore did not have a complete picture of what the sperm transcriptome was like.