Mapping and application of the twin-grain1 gene in rice

Chromosomal inversion at the DG1 promoter drives double-grain spikelets and enhances grain yield in sorghum

The phenomenon of multiple-grain spikelets is frequently observed in gramineous crops. In the case of dual-floret spikelets, the upper fertile floret develops normally to form a single grain, while the lower sterile floret undergoes abortion. Here we elucidate the role of Double-Grain 1 (DG1), a gene encoding a homeobox-domain-containing protein, in regulating the lower floret meristem activity and double-grain spikelet trait in sorghum. A 35.7-kb paracentric inversion in the DG1 promoter region leads to increased DG1 expression, probably by reducing repressive histone modifications. This increase in DG1 expression transforms the degenerated lower floret into a fertile one. The use of the superior DG1 allele results in an increase of approximately 40.7% to 46.1% in grain number per panicle and a 10.1% to 14.3% increase in overall grain yield. Our findings shed light on the sorghum double-grain spikelet characteristic, offering valuable insights for high-yield breeding designs in cereals.

Characterization and fine mapping of Double-grain (Dgs) mutant in sorghum [Sorghum bicolor (L.) Moench]

The sorghum inflorescence is consisted of sessile (SS) and pedicellate spikelets (PS). Commonly, only SS could produce seeds and each spikelet produces one single seed. Here, we identified a sorghum mutant, named Double-grain (Dgs), which can produce twin seeds in each pair of glumes. We characterized the developmental process of inflorescence in Dgs and Jinliang 5 (Jin5, a single-seeded variety) using scanning electron microscope (SEM). The results showed that at the stamen and pistil differentiation stage, Dgs could develop two sets of stamens and carpels in one sessile floret, which resulted in twin-seeded phenotype in Dgs. Two F2 mapping populations derived from the cross between Jin5 and Dgs, and BTx622B and Dgs, were constructed, respectively. The genetic analysis showed that Dgs trait was controlled by a single dominant gene. Through bulk segregation analysis with whole-genome sequencing (BSA-seq) and linkage analysis, Dgs locus was delimited into a region of around 210-kb on chromosome 6, between the markers SSR24 and SSR47, which contained 32 putative genes. Further analysis indicated that Sobic.006G249000 or Sobic.006G249100 may be responsible for the twin-seeded phenotype. This result will be useful for map-based cloning of the Dgs gene and for marker-assisted breeding for increased grain number per panicle in sorghum.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-024-01511-7.

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.