Karl J. Guegler

Genomic Analysis of a Nutrient Response in Arabidopsis Reveals Diverse Expression Patterns and Novel Metabolic and Potential Regulatory Genes Induced by Nitrate

Microarray and RNA gel blot analyses were performed to identify Arabidopsis genes that responded to nitrate at both low (250 μM) and high (5 to 10 mM) nitrate concentrations. Genes involved directly or indirectly with nitrite reduction were the most highly induced by nitrate. Most of the known nitrate-regulated genes (including those encoding nitrate reductase, the nitrate transporter NRT1, and glutamate synthase) appeared in the 40 most strongly nitrate-induced genes/clones on at least one of the microarrays of the 5524 genes/clones investigated. Novel nitrate-induced genes were also found, including those encoding (1) possible regulatory proteins, including an MYB transcription factor, a calcium antiporter, and putative protein kinases; (2) metabolic enzymes, including transaldolase and transketolase of the nonoxidative pentose pathway, malate dehydrogenase, asparagine synthetase, and histidine decarboxylase; and (3) proteins with unknown functions, including nonsymbiotic hemoglobin, a senescence-associated protein, and two methyltransferases. The primary pattern of induction observed for many of these genes was a transient increase in mRNA at low nitrate concentrations and a sustained increase when treated with high nitrate concentrations. Other patterns of induction observed included transient inductions after both low and high nitrate treatments and sustained or increasing amounts of mRNA after either treatment. Two genes, AMT1;1 encoding an ammonium transporter and ANR1 encoding a MADS-box factor, were repressed by nitrate. These findings indicate that nitrate induces not just one but many diverse responses at the mRNA level in Arabidopsis.

Arabidopsis thaliana gene expression microarray services

Incyte has developed a new gene expression microarray (GEM) for analysis of the plant functional genomic system Arabidopsis thaliana. This GEM features over 7,000 array elements from a non-redundant cDNA collection; nearly 30% of the estimated 25,000 genes in this organism. Over 2,000 of these clones represent genes that have functional annotation in public databases. We are offering hybridization and analysis services for the Arabidopsis GEM via Incyte and Genome Systems. Arabidopsis is the primary model system for the study of dicot plant genomics. Academic and commercial groups are using the combination of genomic and genetic tools available for Arabidopsis to study complex problems in plant biology. We have performed a few biological studies using the Arabidopsis GEM to validate the platform and provide examples of possible applications. We will present sample data on these studies.