FUNCTIONAL GENOMICS IN CLOSE WILD RELATIVES OF ARABIDOPSIS THALIANA

这个子项目是众多研究子项目之一

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Now that the entire genome has been sequenced for several model organisms, the next challenge is to identify genes and understand their functions in biologically meaningful contexts (Jackson et al. 2002). The Arabidopsis 2010 project, for example, now seeks to understand the functions of all 25000 Arabidopsis genes within a decade, but to do so, we must understand the role of the natural environment in determining gene function. To better understand gene function and regulation, gene expression can be studied across important ecological gradients. Feeding by insect herbivores, for example, elicits signal transduction and defense responses in plants (Karban and Baldwin 1997), however, relatively little is known about the genes involved in these responses or their expression patterns in other ecological contexts. Although researchers conducting laboratory experiments using Arabidopsis are beginning to understand the role of glucosinolate genes in plant resistance against herbivores (e.g., Jander et al. 2001; Lambrix et al. 2001), ecological genomic studies with close wild relative are needed to better understand the function of these and many other genes (Mitchell-Olds 2001). The genus Arabis, which has recently been split (Al-Shehbaz 2003) into Arabis, Boechera, and Arabidopsis, contains some of the closest wild relatives of Arabidopsis thaliana (Koch et al. 2000). Since the center of diversity of Boechera is in North America (Rollins 1993), we have begun studies on species of Boechera to test general theory on defense evolution (e.g. Jones et al. submitted manuscript; Siemens et al. 2003; Siemens and Roy 2005; Steffes et al. in prep). Our results from these and other studies (Siemens et al. 2002) suggest that resistance and tolerance defensive genes may have other ecological functions, such as increasing plant competitive ability, and that defense responses must be regulated to optimize multiple functions. Here we used the molecular tools of Arabidopsis (microarrays) to identify and understand the function of putative defensive genes and their regulation. Optimality theory for defense evolution (Hamilton et al. 2001 for overview), currently the best framework we have to understand the simultaneous evolution of defense and competitive ability in plants, predicts a tradeoff between defense and competitiveness because defense production is thought to divert limited resources away from competitive growth (Herms and Mattson 1992). We have tested for this evolutionary tradeoff by (1) studying the effects of genetic or environmental variation in defenses on competitive growth, and by (2) studying the effects of genetic variation in competitiveness on defense expression. Although we have detected costs of defenses manifest as reduced growth in the absence of herbivores, these costs were not detected in competitive environments (Siemens et al. 2002; Siemens et al. 2003). That is, defense production affected growth, but not competitive ability. We have also found evidence that measures of defense, such as glucosinolate concentration, were sometimes higher or competitively induced in better competitors. A competitive function for defensive genes would explain many of these results. The genomic tools of Arabidopsis allow us to determine whether competitors induce defensive genes, as one would expect for defenses that also function in competition. A genomic approach also allows a test for the predicted tradeoff between defense and competitive ability, which may further our understanding of gene regulation (Stearns and Magwene 2003).