Abstract: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 T1 and T2 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.(Author for correspondence. Tel: 020 8528 1908; Fax: 020 8528 0200; E-mail: ygliu@scau.edu.cn)