Plant simple sequence repeats: distribution, variation, and effects on gene expression.

Genome-wide simple sequence repeat (SSR) information was analyzed together with functional annotations of Arabidopsis genes and public gene expression data for Arabidopsis and rice. Analysis of more than 15,000 Arabidopsis and more than 16,000 rice SSRs indicated that SSRs may affect the expression of hundreds of genes. Data from experiments on DNA methylation, histone acetylation, and transcript turnover suggest that SSRs may affect gene expression at transcriptional and posttranscriptional levels.

The transcription factor MtSERF1 of the ERF subfamily identified by transcriptional profiling is required for somatic embryogenesis induced by auxin plus cytokinin in Medicago truncatula.

Transcriptional profiling of embryogenic callus produced from Medicago truncatula mesophyll protoplasts indicated up-regulation of ethylene biosynthesis and ethylene response genes. Using inhibitors of ethylene biosynthesis and perception, it was shown that ethylene was necessary for somatic embryogenesis (SE) in this model legume. We chose several genes involved in ethylene biosynthesis and response for subsequent molecular analyses.

Differential response of the plant Medicago truncatula to its symbiont Sinorhizobium meliloti or an exopolysaccharide-deficient mutant.

Sinorhizobium meliloti forms symbiotic, nitrogen-fixing nodules on the roots of Medicago truncatula. The bacteria invade and colonize the roots through structures called infection threads. S.

Transcript analysis of early nodulation events in Medicago truncatula.

Within the first 72 h of the interaction between rhizobia and their host plants, nodule primordium induction and infection occur. We predicted that transcription profiling of early stages of the symbiosis between Medicago truncatula roots and Sinorhizobium meliloti would identify regulated plant genes that likely condition key events in nodule initiation. Therefore, using a microarray with about 6,000 cDNAs, we compared transcripts from inoculated and uninoculated roots corresponding to defined stages between 1 and 72 h post inoculation (hpi).

Development and mapping of SSR markers for maize.

Microsatellite or simple sequence repeat (SSR) markers have wide applicability for genetic analysis in crop plant improvement strategies. The objectives of this project were to isolate, characterize, and map a comprehensive set of SSR markers for maize (Zea mays L.).

Expanding the genetic map of maize with the intermated B73 x Mo17 (IBM) population.

The effects of intermating on recombination and the development of linkage maps were assessed in maize. Progeny derived from a common population (B73 x Mo17) before and after five generations of intermating were genotyped at the same set of 190 RFLP loci. Intermating resulted in nearly a four-fold increase in the genetic map distance and increased the potential for improved genetic resolution in 91% of the intervals evaluated.