WOOD DEVELOPMENT - EST DATABASES PROVIDE INSIGHT INTO GENE FUNCTION

Dept. of Forest Science and Crop Biotechnology Center, Texas A&M University, College Station, TX 77843-2135

Arabinogalactan-proteins (AGPs) are a group of proteoglycans postulated to play important roles in plant development. Several possible roles are particularly intriguing with regard to wood development. We have cloned and characterized three AGPs preferentially expressed in differentiating xylem of loblolly pine. Other AGP-like genes have been identified in a loblolly pine EST collection. This presentation will discuss how genomics projects involving various species have complemented the biochemistry and molecular biology done in our lab to determine the roles of AGPs in xylogenesis. Likewise work done in our lab has helped with the identification of AGPs in the databases. One example is PtaAGP3, an AGP purified and sequenced in our laboratory. Access to a loblolly pine EST library provided us with a full-length clone corresponding to our protein. The protein sequencing identified the clone as encoding an AGP and identified an unexpected protein cleavage site. A second example is PtX14A9. C-myc tagged versions of two putative AGPs, PtX3H6 and PtX14A9, were expressed in transgenic tobacco and purified proteins used to determine the genes encode AGPs. An ortholog of PtX14A9 was cloned from poplar and similar proteins from many species identified in the EST databases. Our work assigned an identity to numerous ESTs while at the same time, the information about the ESTs has provided clues as to the role PtX14A9 plays in development. A 14A9-like protein was cloned from soybean following the screening of a cDNA library using antibodies to plasma membrane proteins, confirming our hypothesis that PtX14A9 is at least temporarily localized on the plasma membrane. ESTs encoding proteins very similar to PtX14A9 are preferentially expressed in poplar xylem, arabidopsis stems, and cotton fibers. The expression in cotton fibers suggests PtX14A9 may have a role in cell elongation or secondary cell wall deposition.