PROGRESS IN GENOMIC ANALYSIS OF THE SOYBEAN SUPERNODULATION MUTATION nts-1.

¹ The University of Tennessee, Plant Molecular Genetics and Center for Legume Research, 269 Plant Science Building, P.O. Box 1071, Knoxville, TN 37901-1071 USA

² The Noble Foundation, 2510 Sam Noble Parkway P.O. Box 2180 Ardmore, OK 73402 USA

³ Department of Plant Soil and General Agriculture, Southern Illinois University at Carbondale, Carbondale, IL 62901-4415 USA

This project focuses on the positional cloning of the soybean NTS-1 (also labeled rj7) gene (Linkage Group H, USDA map). Mutation at the locus causes "supernodulation" phenotype, and nodulation of mutant plants is not inhibited by nitrate. The NTS-1 locus governs the systemic autoregulation response that controls nodule number through production of a presumptive shoot-derived inhibitor. Two flanking molecular markers, pUTG132a (0.4 cM to the gene) and pA381 (3.1 cM to the gene) are being used as anchors in the positional cloning of NTS-1. We have started to generate BAC contigs containing NTS-1 using two independently constructed BAC libraries. In parallel, we have started to analyze transcription (EST) density of the NTS-1 region. The 5'-end of the pA381 marker shows a high homology to several Arabidopsis, potato and Ricinus communis amino acid permeases. One of the homologous Arabidopsis clones maps to chromosome 5 of Arabidopsis. The soybean pA381 PCR primers also amplify products from Arabidopsis DNA (Col and Ler) giving the possibility of a microsynteny between soybean and Arabidopsis in the NTS-1 region. Additionally, recently two soybean ESTs expressed in young leaves were mapped close to the pUTG132a marker (Dr. K. Harada, Chiba University, Japan). Since supernodulation is a shoot-controlled trait, most probably expressing in leaves, the possibilities of co-mapping of two ESTs and NTS-1, as well as their functional relationships are being tested. The work is supported by Tennessee Soybean Promotion Board and partially by USDA.