Fine Mapping And Cloning Of The Rice Bentazon Resistance Gene Bel

Bentazon have been used for selective control of broadleaf weeds and sedges in ricefields for more than 20 years. A bentazon susceptible mutant, bel, was previouslyidentified for the purpose of allowing these herbicides to be used for removing falsehybrids from hybrid rice. Using 1,776 susceptible plants from a population ofapproximately 8000 F₂ individuals, we constructed a fine map for the Bel locus anddelimited it to a 36kb DNA fragment between two RFLP makers, L5 and P17.Bioinformatic analysis indicated that there are five genes within this interval, anethylene-responsive OsER33 gene and four tandem repeats of cytochrome P450 genesdesignated as CYP81A5, CYP81A6, CYP81A7 and CYP81A8, respectively. Comparativesequencing could not find any differences in the coding regions of the OsER33,CYP81A5,CYP81A7 and CYP81A8 genes between the mutant bel and its wild-typeprogenitor W6154S, but did identify a single base G deletion at position+1,332 bpdownstream from the translation start codon of CYP81A6. This deletion introduces apremature stop codon and leads to the loss of the heme-binding motif, which is essentialfor cytochrome P450 function because it contain an absolutely conserved cysteine thatserves as the fifth ligand to the heme iron. CYP81A6 presumably functions as ahydroxylase for the detoxification of bentazon herbicides in rice. A genespecific cleavedamplified polymorphic sequence marker and tightly linked flanking marker weredeveloped that will be very useful for selection of the bel allele transferred tophotoperiod-/thermo-sensitive genic male sterility and CMS lines in hybrid rice breedingprograms.