INTRAGENIC RECOMBINATION IN THE CSR1 LOCUS OF ARABIDOPSIS

Four classes of herbicides are known to inhibit plant acetolactate syn thase (ALS). In Arabidopsis, ALS is encoded by a single gene, CSR1. Th e dominant csr1-1 allele encodes an ALS resistant to chlorsulfuron and triazolopyrimidine sulfonamide while the dominant csr1-2 allele encod es an ALS resistant to imazapyr and pyrimidyl-oxy-benzoate. The molecu lar distance between the point mutations in csr1-1 and csr1-2 is 1369 bp. Here we used multiherbicide resistance as a stringent selection to measure the intragenic recombination frequency between these two poin t mutations. We found this frequency to be 0.008 +/- 0.0028. The recom binant multiherbicide-resistant allele, csr1-4, provides an ideal mark er for plant genetic transformation.