Plant Model Systems

Considerably more progress has been made toward our understanding of plant genes to date because of the higher investment that has been made in plant biology. From 1985-1995, the Rockefeller Foundation sponsored an international research program in rice biotechnology that led to the generation of rice molecular maps, transformation of rice, and the characterization of many basic biochemical pathways for abiotic stress and disease and insect resistance in rice. The United States National Science Foundation (NSF)-Arabidopsis 2010 and Plant Genome Initiatives have also had a major impact on plant science research in the last decade (Ausubel 2002). Many of the projects deal with how Arabidopsis responds to and resists pathogens such as: (a) the Arabidopsis RPM1 disease resistance signaling network; (b) expression profiling of plant disease resistance pathways; (c) functional and comparative genomics of NBS-LRR-encoding genes; (d) Functional genomics of quantitative traits. Expression level polymorphisms (ELPs) of QTLs affecting disease resistance pathways in Arabidopsis; and (e) the endgame for research genetics. Isolation and distribution of a knockout mutant for every gene in Arabidopsis. More information can be obtained at the web sites of these projects (Ausubel 2002). National Science Foundation Plant Genome has also funded allied work in other crops plants (httn:// This research represents the cutting edge of plant science using the latest tools: microarrays to study gene expression, T-DNA insertion mutants, large scale mutant hunts, molecular mapping, and structure-function analysis of genes at the whole genome level.

High through put methods for creating mutants using gene silencing that allow gene libraries or cDNA collections to be cloned in a silencing vector using an in vitro recombinase should facilitate systematic functional analysis of plant genes in plant defense (Wesley et al. 2001). Conventional mutagenesis of plants carrying a construct such as a luciferase or GUS (^-glucuronidase) reporter gene under the control of a defense gene promoter are yielding new and interesting classes of mutants with constitutive broad-spectrum disease resistance (Maleck et al. 2002). These mutants showed strong resistance to P. parasitica isolates Noco2 and Emco5 and variable resistance to Elysiphe cichoracearum. In addition to T-DNA, endogenous and heterologous plant transposable elements are being used to systematically mutate the rice genome and isolate promoter elements via enhancer trapping elements (Greco et al. 2001; Hirochika et al. 2001). The transcriptome of Arabidopsis has been characterized during systemic acquired resistance (Maleck et al. 2000). Analysis of 402 putative transcription factors from Arabidopsis using OMAs allowed the identification of transcription factors that may be involved in regulation of various pathways responsive to environmental stress and bacterial infection (Chen et al. 2002). These systems level approaches to analysis of model plants are expected to yield an integrated view of how every gene contributes to the growth and development and defense of plants.

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