Phenotypic Characterization, Genetic Analysis and Molecular Mapping of a New Floral Organ Mutant Gene in Rice

Abstract

A rice floral organ mutant, srs2, derived from a spontaneous mutation, was first discovered in a japonica rice variety GNZ. The mutant displayed various abnormalities in floral organ including longer paleas/lemmas, split spikelets, palea/lemma-like lodicules, two florets of the same rachilla, a decrease in stamen number, and an increase in pistil number. Moreover, the seed-setting rate of the mutant was also reduced to 9.8%. Observations of the floral organ morphogenesis by a scanning electron microscope (SEM) in the mutant indicated that the development of androecium and gynoecia was abnormal and an additional floret and several palea/lemma-like lodicules were usually formed by the irregular development of the floral meristem. Genetic analysis of 4 F2 and 2 BC1F1 populations showed that the mutation was controlled by a single recessive gene, and designated as srs2 (spit rice spikelet 2). Screening of 643 F2 mutant individuals derived from the cross of srs2 × 202R with simple sequence repeat (SSR) markers demonstrated that SRS2 is located between the molecular marker S31 and L75, at a distances of 0.07 and 2 cM, respectively, on chromosome 3. The SRS2 gene was also discussed to be a new floral organ identity gene in rice.