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Iron deficiency leads to severe chlorosis in crop plants, including wheat, thereby reducing total yield and quality. Furthermore, grains of most bread wheat varieties are poor source of iron, which is vital for human nutrition. Despite the significance, iron uptake and translocation mechanisms in bread wheat have not been studied in detail, particularly under iron limited growth conditions. In this study, bread wheat plants were grown under iron deficiency stress until maturity. Data were collected at three distinct developmental time points during grain-filling. The plants experiencing low iron availability exhibited significantly lower chlorophyll content as well as low iron concentration in leaves and grains. The expression levels of bread wheat genes homologous to iron deficiency responsive genes of rice, barley, and Arabidopsis were significantly changed under iron deficiency stress. The wheat homologs of genes involved in phytosiderophore (PS) synthesis and transport were significantly up-regulated in the iron-deficient roots through all development stages, confirming an important role of deoxymugineic acid (DMA) in iron acquisition. The up-regulation of NICOTIANAMINE SYNTHASE (NAS) and DEOXYMUGINEIC ACID SYNTHASE (DMAS) in flag leaves and grains suggested the involvement of nicotianamine (NA) and DMA in iron chelation and translocation in wheat, particularly at the commencement of grain-filling. In line with this, the homolog of gene encoding TRANSPORTER OF MUGINEIC ACID (TOM) was up-regulated in the wheat roots under iron deficiency. Additionally, genes encoding long-distance iron transporter YELLOW STRIPE-LIKE (YSL), the vacuolar transporter NATURAL RESISTANCE ASSOCIATED MACROPHAGE PROTEIN (NRAMP), and the transcription factor BASIC HELIX-LOOP-HELIX (bHLH), were also up-regulated upon iron starvation. A tissue specific and growth stage specific gene expression differences in response to iron deficiency stress were observed, providing new insights into iron translocation, storage and regulation in bread wheat.

Rice is a major cereal crop that contributes significantly to global food security. Biotic stresses, including the rice blast fungus, cause severe yield losses that significantly impair rice production worldwide. The rapid genetic evolution of the fungus often overcomes the resistance conferred by major genes after a few years of intensive agricultural use. Therefore, resistance breeding requires continuous efforts of enriching the reservoir of resistance genes/alleles to effectively tackle the disease. Seed banks represent a rich stock of genetic diversity, however, they are still under-explored for identifying novel genes and/or their functional alleles. We conducted a large-scale screen for new rice blast resistance sources in 4246 geographically diverse rice accessions originating from 13 major rice-growing countries. The accessions were selected from a total collection of over 120’000 accessions based on their annotated rice blast resistance information in the International Rice Genebank. A two-step resistance screening protocol was used involving natural infection in a rice uniform blast nursery and subsequent artificial infections with five single rice blast isolates. The nursery-resistant accessions showed varied disease responses when infected with single isolates, suggesting the presence of diverse resistance genes/alleles in this accession collection. In addition, 289 accessions showed broad-spectrum resistance against all five single rice blast isolates. The selected resistant accessions were genotyped for the presence of the Pi2 resistance gene, thereby identifying potential accessions for isolation of allelic variants of this blast resistance gene. Together, the accession collection with broad spectrum and isolate specific blast resistance represent the core material for isolation of previously unknown blast resistance genes and/or their allelic variants that can be deployed in rice breeding programs.

Nearly one-third of the world population, mostly women and children, suffer from iron malnutrition and its consequences, such as anemia or impaired mental development. Biofortification of rice, which is a staple crop for nearly half of the world’s population, can significantly contribute in alleviating iron deficiency. NFP rice (transgenic rice expressing nicotianamine synthase, ferritin and phytase genes) has a more than six-fold increase in iron content in polished rice grains, resulting from the synergistic action of nicotianamine synthase (NAS) and ferritin transgenes. We investigated iron homeostasis in NFP plants by analyzing the expression of 28 endogenous rice genes known to be involved in the homeostasis of iron and other metals, in iron-deficient and iron-sufficient conditions. RNA was collected from different tissues (roots, flag leaves, grains) and at three developmental stages during grain filling. NFP plants showed increased sensitivity to iron-deficiency conditions and changes in the expression of endogenous genes involved in nicotianamine (NA) metabolism, in comparison to their non-transgenic siblings. Elevated transcript levels were detected in NFP plants for several iron transporters. In contrast, expression of OsYSL2, which encodes a member of Yellow Stripe-like protein family, and a transporter of the NA-Fe(II) complex was reduced in NFP plants under low iron conditions, indicating that expression of OsYSL2 is regulated by the endogenous iron status. Expression of the transgenes did not significantly affect overall iron homeostasis in NFP plants, which establishes the engineered push-pull mechanism as a suitable strategy to increase rice endosperm iron content.