A rice panicle mutant created by transformation with an antisense cDNA library

A rice (Oryza sativa L.) mutant displaying defects in panicle development was identified among transformants in a transgenic mutagenized experiment using an antisense cDNA library prepared from young rice panicles. In the mutant, the average spikelet number was reduced to 59.8 compared with 104.3 in wild-type plants. In addition, the seed-setting rate of the mutant was low (39.3%) owing to abnormal female development. Genetic analysis of T-1 and T-2 progeny showed that the traits segregated in a 3 (mutant): 1 (wild type) ratio and the mutation was cosegregated with the transgene. Southern blot and thermal asymmetric interlaced polymerase chain reaction analyses showed that the mutant had a single T-DNA insertion on chromosome 5, where no gene was tagged. Sequencing analysis found that the transgenic antisense cDNA was derived from a gene encoding an F-box protein in chromosome 7 with unidentified function. This and another four homologous genes encoding putative F-box proteins form a gene cluster. These results indicate that the phenotypic mutations were most likely due to the silencing effect of the expressed transgenic antisense construct on the member(s) of the F-box gene cluster.