Adapting rice anther culture to gene transformation and RNA interference

CF1 reduces grain-cadmium levels in rice (Oryza sativa)

Rice (Oryza sativa) is a leading source of dietary cadmium (Cd), a non-essential heavy metal that poses a serious threat to human health. There are significant variations in grain-Cd levels in natural rice populations, which make the breeding of low-Cd rice a cost-effective way to mitigate grain-Cd accumulation. However, the genetic factors that regulate grain-Cd accumulation have yet to be fully established, thereby hindering the development of low-Cd varieties. Here, we reported a low-Cd quantitative trait locus, CF1, that has the potential to reduce Cd accumulation in rice grains. CF1 is allelic to the metal transporter OsYSL2, which transports Fe from the roots to the shoots. However, it is incapable of binding Cd, and thus, reduces grain-Cd levels indirectly rather than directly in the form of upward delivery. Further analysis showed that high expression levels of CF1 improve Fe nutrition in the shoots, subsequently inhibiting Cd uptake by systemically inhibiting expression of the main Cd uptake gene OsNramp5 in the roots. Compared with the CF1 allele from '02428' (CF1⁰²⁴²⁸ ), higher expression levels of CF1 from 'TQ' (CF1^TQ ) increased the Fe contents and decreased Cd levels in rice grains. In natural rice populations, CF1^TQ was found to be a minor allele, while CF1⁰²⁴²⁸ is present in most japonica rice, suggesting that CF1^TQ could be widely integrated into the japonica rice genome to generate low-Cd varieties. Overall, these results broaden our mechanistic understanding of the natural variation in grain-Cd accumulation, supporting marker-assisted selection of low-Cd rice.

P, B. N. D, Samantaray S. Androgenesis in indica rice: A comparative competency in development of doubled haploids

Rice is critical to global food security which demands immediate attention to meet the ever-growing population. Development of improved variety is the major focus area of research, in which doubled haploid (DH) technology plays a vital role. Since, androgenesis shows its potential in DH production, this method was not capitalized specially in indica rice due to due to its recalcitrant nature to tissue culture. Success of androgenesis is governed by many important factors such as stage of anther, pre-treatment conditions, accurate concentrations of media, and plant growth regulators. Though reports of androgenesis are abundant in rice, most of them either used japonica or a specific cultivar of indica rice ecotypes. In this study, a media combination was established which is successful in producing doubled haploids from F₁s of Savitri x Pokkali, IR20 x Mahulata along with the popular indica hybrids of Arize 8433DT, Arize 6453, Arize Bold, and Swift Gold. Out of 12 different media combinations tested, and 5 different durations of cold-treatments studied, N6 media with 2,4-D (2.0 mg/l) and BAP (0.5 mg/l) with 7^th day cold pre-treatment was found to be most effective in all of the F₁s for callus induction. Among all the F₁s, rice hybrid, Arize 8433DT showed highest of 52% callus induction. In case of green shoot regeneration, MS media with NAA (0.5 mg/l), BAP (2.0 mg/l) and Kn (1.0 mg/l) (MS+C4) was found to be the most efficient of six treatments studied with highest of 58.25% regeneration in Arize 8433DT. Further, MS+C4 in combination with proline (5.0 mg/l) increased the regeneration rate to 85.99%. Besides, MS media with NAA (1.0 mg/l), Kn (0.1 mg/l) and 50 g/l sucrose was found to be most efficient for supporting root induction in all F1s. This study claims the establishment of genotype independent androgenic protocol for indica rice which could be capitalized in indica rice improvement.

Homozygous Transgenic Barley (Hordeum vulgare L.) Plants by Anther Culture

Production of homozygous lines derived from transgenic plants is one of the important steps for phenotyping and genotyping transgenic progeny. The selection of homozygous plants is a tedious process that can be significantly shortened by androgenesis, cultivation of anthers, or isolated microspores. Doubled haploid (DH) production achieves complete homozygosity in one generation. We obtained transgenic homozygous DH lines from six different transgenic events by using anther culture. Anthers were isolated from T0 transgenic primary regenerants and cultivated in vitro. The ploidy level was determined in green regenerants. At least half of the 2n green plants were transgenic, and their progeny were shown to carry the transgene. The process of dihaploidization did not affect the expression of the transgene. Embryo cultures were used to reduce the time to seed of the next generation. The application of these methods enables rapid evaluation of transgenic lines for gene function studies and trait evaluation.

Haploids in flowering plants: origins and exploitation

The first haploid angiosperm, a dwarf form of cotton with half the normal chromosome complement, was discovered in 1920, and in the ninety years since then such plants have been identified in many other species. They can occur either spontaneously or can be induced by modified pollination methods in vivo, or by in vitro culture of immature male or female gametophytes. Haploids represent an immediate, one-stage route to homozygous diploids and thence to F(1) hybrid production. The commercial exploitation of heterosis in such F(1) hybrids leads to the development of hybrid seed companies and subsequently to the GM revolution in agriculture. This review describes the range of techniques available for the isolation or induction of haploids and discusses their value in a range of areas, from fundamental research on mutant isolation and transformation, through to applied aspects of quantitative genetics and plant breeding. It will also focus on how molecular methods have been used recently to explore some of the underlying aspects of this fascinating developmental phenomenon.

STAMENLESS 1, encoding a single C2H2 zinc finger protein, regulates floral organ identity in rice

Floral organ identity is defined by organ homoetic genes whose coordinated expression is crucial with respect to the time and place of floral organ formation. Here, we report molecular cloning and characterization of the rice STAMENLESS 1 (SL1) gene that is involved in floral development. The sl1 mutant largely resembles the rice B-class gene mutant spw1; both exhibit homeotic conversions of lodicules and stamens to palea/lemma-like organs and carpels. Additionally, sl1 produces flowers with varied numbers of inner floral organs, and amorphous tissues without floral organ identity were frequently formed in whorls 3 and 4. We also show that SL1 specifies lodicule and stamen identities through positive transcriptional regulation of SPW1/OsMADS16 expression. SL1 encodes a member of the C2H2 family of zinc finger proteins, closely related to JAG of Arabidopsis. The functional divergence between SL1 and JAG implies that SL1 was co-opted for its distinctive roles in specification of floral organ identity in rice after the lineage split from Arabidopsis.

The ploidy effects in plant gene expression: progress, problems and prospects

Polyploidy and haploid are widely employed in the studies of genetics and evolution, and great progress has been made in these fields, inspiring the enthusiasm of scientists to explore the ploidy effects in gene expression. In this paper, we review the gene expression and its regulation in polyploids, especially in autopolyploids. We summarize some limitations in previous reports on polyploidy gene expression and its regulation, especially the limitations in the research materials. We propose an idea to create homologous ploidy series with twin-seedlings and to employ high-throughput techniques to investigate the polyploidy transcriptome and its regulation.