A weak allele of TGW5 enables greater seed propagation and efficient size-based seed sorting for hybrid rice production

Background China has been successful in breeding hybrid rice strains, but is now facing challenges to develop new hybrids with high-yielding potential, better grain quality, and tolerance to biotic and abiotic stresses. This paper reviews the most significant advances in hybrid rice breeding in China, and presents a recent study on fine-mapping quantitative trait loci (QTLs) for yield traits. Scope By exploiting new types of male sterility, hybrid rice production in China has become more diversified. The use of inter-subspecies crosses has made an additional contribution to broadening the genetic diversity of hybrid rice and played an important role in the breeding of super rice hybrids in China. With the development and application of indica-inclined and japonica-inclined parental lines, new rice hybrids with super high-yielding potential have been developed and are being grown on a large scale. DNA markers for subspecies differentiation have been identified and applied, and marker-assisted selection performed for the development of restorer lines carrying disease resistance genes. The genetic basis of heterosis in highly heterotic hybrids has been studied, but data from these studies are insufficient to draw sound conclusions. In a QTL study using stepwise residual heterozygous lines, two linked intervals harbouring QTLs for yield traits were resolved, one of which was delimited to a 125-kb region. Conclusions Advances in rice genomic research have shed new light on the genetic study and germplasm utilization in rice. Molecular marker-assisted selection is a powerful tool to increase breeding efficiency, but much work remains to be done before this technique can be extended from major genes to QTLs.

It has been shown that the disruption of the alpha-subunit gene of heterotorimeric G-proteins (Galpha) results in dwarf traits, the erection of leaves and the setting of small seeds in rice. These mutants are called d1. We have studied the expression profiles of the transcripts and translation products of rice Galpha in ten alleles of d1 including five additional alleles newly identified. By RT-PCR, the transcripts of the Galpha gene were detected in the all d1 alleles. By western blot, the Galpha proteins were not detected in the plasma membrane fractions of the d1 alleles with the exception of d1-4. In d1-4, one amino acid change in the GTP-binding box A of the Galpha protein was occurred and even in this case the Galpha protein was only just detectable in the plasma membrane fraction. Given that the Galpha protein did not accumulate in the plasma membrane fraction in d1-8 which has a deletion of just a single amino acid in the Galpha protein, it is likely that a proper conformation of the Galpha is necessary for accumulation of Galpha protein in the plasma membrane. Nine alleles of d1 showed a severer phenotype whilst d1-4 exhibited a mild phenotype with respect to seed size and elongation pattern of internodes. As brassinosteroid signaling was known to be partially impaired in d1s, the sensitivity to 24-epibrassinolide (24-epiBL) was compared among d1 alleles in a T65 genetic background. Only d1-4 showed responses similar to wild type rice. The results show that the d1-4 mutant is a mild allele in terms of the phenotype and mild hyposensitivity to the exogenously applied 24-epiBL.

Background The breeding and large-scale adoption of hybrid rice is an important achievement in modern agriculture. Mechanized seed production is urgently needed for widespread adoption of hybrid rice because it can compensate for the shortage of manual labor to meet the growing food demands in China. Results Here, we report the development of a mechanized hybrid rice seed production method using a female sterile rice. In this method, three closely linked gene expression cassettes were introduced into female sterile rice. The three expression cassettes are: 1) a rice female fertility gene expression cassette; 2) a pollen-lethal gene expression cassette; and 3) a red fluorescence protein gene expression cassette. During the self-fertilization process of a heterozygous transgenic rice plant, pollen grains carrying the transgene die off and cannot participate in fertilization; pollen grains not carrying a transgene can normally fertilize the female gamete, leading to fructification. By means of fluorescence-assisted sorting, homogeneous female sterile rice seeds are sorted out from other seeds carrying the transgene and are used for mechanized hybrid rice seed production; heterozygous seeds carrying the transgene can then be used in the multiplication of female sterile rice. Conclusions This technology solves the difficulty of multiplying female-sterile rice, allows for mechanized production of hybrid rice seed, and will prove especially valuable in systems using a mixed-planting, mixed-harvesting approach. Moreover, it uses transgenic technology that has not yet been employed in a seed production process in which the output is non-transgenic seeds.