Rice backcross population assessment for iron tolerance through phenotypic and genotypic analyses

Iron toxicity has become a serious issue affecting rice (Oryza sativa L.) production in many irrigated lowland areas. The selection of Fe2+-tolerant rice cultivars under iron toxicity conditions and the identification of molecular markers are good approaches to obtaining tangible results. This study aimed to identify simple sequence repeat (SSR) markers that were associated with iron tolerance traits in a rice backcross population. A total of 117 seedlings from the backcross (BC3F2) of ‘OM6830’/‘AS996’//‘AS996’ were phenotyped at the 4-week-seedling stage at Ton Duc Thang University, Ho Chi Minh City, Vietnam. The rice population was screened in Yoshida nutrient medium supplemented with FeCl2 at a concentration of 150 mg L−1 under greenhouse conditions. Phenotypic analysis was conducted by scoring two parameters, namely, root length and leaf bronzing. Genotypic analysis was carried out on the BC3F2 population by using four markers, i.e., RM6, RM240, RM252, and RM451, for association analysis with iron tolerance. A total of 23 BC3F2 lines were selected on the basis of their higher tolerance (score 1) for Fe2+ compared with the tolerant parental line ‘AS996’. The markers RM6 and RM240 were highly polymorphic and identified different Fe2+-tolerant lines in the BC3F2 population. Among the BC3F3 progeny derived from the selected 23 BC3F2 lines, BC3F3-7 was identified as the most Fe2+-tolerant line. BC3F3-15 was also found to be Fe2+ tolerant. Both lines showed good development capability and provided high yields under stress conditions. These tolerant BC3F3 lines could be further screened with additional SSR markers in future breeding programs aiming to increase rice production in iron-contaminated areas of the Mekong Delta, Vietnam.

Yap5 Competes With Hap4 for the Regulation of Iron Homeostasis Genes in the Human Pathogen Candida glabrata

The CCAAT-binding complex (CBC) is a conserved heterotrimeric transcription factor which, in fungi, requires additional regulatory subunits to act on transcription. In the pathogenic yeast Candida glabrata, CBC has a dual role. Together with the Hap4 regulatory subunit, it activates the expression of genes involved in respiration upon growth with non-fermentable carbon sources, while its association with the Yap5 regulatory subunit is required for the activation of iron tolerance genes in response to iron excess. In the present work, we investigated further the interplay between CBC, Hap4 and Yap5. We showed that Yap5 regulation requires a specific Yap Response Element in the promoter of its target gene GRX4 and that the presence of Yap5 considerably strengthens the binding of CBC to the promoters of iron tolerance genes. Chromatin immunoprecipitation (ChIP) and transcriptome experiments showed that Hap4 can also bind these promoters but has no impact on the expression of those genes when Yap5 is present. In the absence of Yap5 however, GRX4 is constitutively regulated by Hap4, similarly to the genes involved in respiration. Our results suggest that the distinction between the two types of CBC targets in C. glabrata is mainly due to the dependency of Yap5 for very specific DNA sequences and to the competition between Hap4 and Yap5 at the promoter of the iron tolerance genes.

Chromosomal introgressions from Oryza meridionalis into domesticated rice Oryza sativa result in iron tolerance

Iron (Fe) toxicity is one of the most common mineral disorders affecting rice (Oryza sativa) production in flooded lowland fields. Oryza meridionalis is indigenous to northern Australia and grows in regions with Fe-rich soils, making it a candidate for use in adaptive breeding. With the aim of understanding tolerance mechanisms in rice, we screened a population of interspecific introgression lines from a cross between O. sativa and O. meridionalis for the identification of quantitative trait loci (QTLs) contributing to Fe-toxicity tolerance. Six putative QTLs were identified. A line carrying one introgression from O. meridionalis on chromosome 9 associated with one QTL was highly tolerant despite very high shoot Fe concentrations. Physiological, biochemical, ionomic, and transcriptomic analyses showed that the tolerance of the introgression lines could partly be explained by higher relative Fe retention in the leaf sheath and culm. We constructed the interspecific hybrid genome in silico for transcriptomic analysis and identified differentially regulated introgressed genes from O. meridionalis that could be involved in shoot-based Fe tolerance, such as metallothioneins, glutathione S-transferases, and transporters from the ABC and MFS families. This work demonstrates that introgressions of O. meridionalis into the O. sativa genome can confer increased tolerance to excess Fe.

Introgression from Oryza meridionalis into domesticated rice Oryza sativa results in shoot-based iron tolerance

Iron (Fe) toxicity is one of the most common mineral disorders affecting rice (Oryza sativa) production in flooded lowland fields. Oryza meridionalis is endemic from Northern Australia and grows in regions with Fe rich soils, making it a candidate for use in adaptive breeding. Aiming to understand tolerance mechanisms in rice, we screened a population of interspecific introgression lines (IL) from a cross between O. sativa and O. meridionalis for the identification of QTLs contributing to Fe toxicity tolerance. Six putative QTLs were identified. A line carrying one introgression from O. meridionalis on chromosome 9 associated with one QTL was highly tolerant despite very high shoot Fe concentrations. Physiological, biochemical, ionomic and transcriptomic analyses showed that the IL tolerance could partly be explained by Fe retention in the leaf sheath and culm. We constructed the interspecific hybrid genome in silico for transcriptomic analysis, and identified differentially regulated introgressed genes from O. meridionalis that could be involved in shoot-based Fe tolerance, such as metallothioneins, glutathione S-transferases and transporters from ABC and MFS families. This is the first work to demonstrate that introgressions of O. meridionalis into the O. sativa genome can confer increased tolerance to excess Fe.HighlightWe identified QTLs associated with iron tolerance derived from O. meridionalis, and characterized their physiological basis in O. sativa.