Mapping and application of the twin-grain1 gene in rice

Identification and characterization of a novel gene controlling floral organ number in rice (Oryza sativa L.)

Floral organ number is crucial for successful seed setting and mature grain development. Although some genes and signaling pathways controlling floral organ number have been studied, the underlying mechanism is complicated and requires further investigation. In this study, a floral organ number mutant was generated by the ethyl methanesulfonate treatment of the Korean japonica rice cultivar Ilpum. In the floral organ number mutant, 37% of the spikelets showed an increase in the number of floral organs, especially stamens and pistils. Histological analysis revealed that the number of ovaries was determined by the number of stigmas; spikelets with two or three stigmas contained only one ovary, whereas spikelets with four stigmas possessed two ovaries. The floral organ number mutant showed pleiotropic phenotypes including multiple grains, early flowering, short plant height, and reduced tiller number compared with the wild-type. Genetic and MutMap analyses revealed that floral organ number is controlled by a single recessive gene located between the 8.0 and 20.0 Mb region on chromosome 8. Calculation of SNP-index confirmed Os08g0299000 as the candidate gene regulating floral organ number, which was designated as FLORAL ORGAN NUMBER7 (FON7). A single nucleotide polymorphism (G to A) was discovered at the intron splicing donor site of FON7, which caused the skipping of the entire sixth exon in the mutant, resulting in the deletion of 144 bp. Furthermore, the T-DNA-tagged line displayed the same floral organ number phenotype as the fon7 mutant. These results provide valuable insight into the mechanism of floral organ differentiation and formation in rice.

Morphological and proteomic analysis of young spikes reveals new insights into the formation of multiple-pistil wheat

A new multiple-pistil wheat mutant germplasm with more than one pistil in a floret was obtained from natural mutagenesis. This mutant can develop 2-3 grains in a glume after pollination and has a significant grain number advantage compared with normal wheat. However, the basis of the formation of multiple-pistil wheat has thus far not been well established. In this study, we first performed a continuous phenotypic observation of the floral meristem (FM) in multiple-pistil wheat. The results indicated that the secondary pistils are derived from extra stem cells that fail to terminate normally between the carpel primordium and the lodicule primordium. To further probe the potential molecular basis for the formation of secondary pistils, comparative proteomic analyses were conducted. A total of 334 differentially abundant proteins (DAPs) were identified using isobaric tags for relative and absolute quantification (iTRAQ), among which 131 proteins were highly abundant and 203 proteins were less abundant in the young spikes of multiple-pistil wheat. The DAPs, located primarily in the cell, were involved in the translation and the metabolisms of carbohydrate, nucleotide, and amino acid. Differential expression analysis showed that TaHUA2, TaRF2a, TaCHR12 and TaHEN2 may play vital roles in the regulation of wheat flower organ number. In general, the DAPs support the phenotypic analysis results at the molecular level. In combination, these results reveal new insights into the formation of multiple-pistil wheat and provide possible targets for further research on the regulation of floral organ number in wheat.