Screening Arabidopsis accessions for alkaline stress tolerance

RESEARCH QUESTIONS 1. Will there be differences between Arabidopsis accessions for alkaline stress tolerance in potting mix growth conditions? 2. Will there be differences for fluorescent concentration between inside and outside roots in hydroponic system? 3. Will there be differences for fluorescent concentration between different Arabidopsis accessions in hydroponic system

Screening Arabidopsis accessions for alkaline stress tolerance

RESEARCH QUESTIONS 1. Will there be differences between Arabidopsis accessions for alkaline stress tolerance in potting mix growth conditions? 2. Will there be differences for fluorescent concentration between inside and outside roots in hydroponic system? 3. Will there be differences for fluorescent concentration between different Arabidopsis accessions in hydroponic system

Ethylene production, cluster root formation, and localization of iron(III) reducing capacity in Fe deficient squash roots

Dicots and non-graminaceous monocots have the ability to increase root iron(III) reducing capacity in response to iron (Fe) deficiency stress. In squash (Cucurbita pepo L.) seedlings, Fe(III) reducing capacity was quantified during early vegetative growth. When plants were grown in Fe-free solution, the Fe(III) reducing capacity was greatly elevated, reached peak activity on day 4, then declined through day 6. Root ethylene production exhibited a temporal pattern that closely matched that of Fe(III) reducing capacity through day 6. On the 7th day of Fe deficiency, cluster root morphology developed, which coincided with a sharp increase in the root Fe(III) reducing capacity, although ethylene production decreased. Localization of Fe(III) reducing capacity activity was observed during the onset of Fe deficiency and through the development of the root clusters. It was noted that localization shifted from an initial pattern which occurred along the main and primary lateral root axes, excluding the apex, to a final localization pattern in which the reductase appeared only on secondary laterals and cluster rootlets

Alkaline stress and iron deficiency regulate iron uptake and riboflavin synthesis gene expression differently in root and leaf tissue: implications for iron deficiency chlorosis

Iron (Fe) is an essential mineral that has low solubility in alkaline soils, where its deficiency results in chlorosis. Whether low Fe supply and alkaline pH stress are equivalent is unclear, as they have not been treated as separate variables in molecular physiological studies. Additionally, molecular responses to these stresses have not been studied in leaf and root tissues simultaneously. We tested how plants with the Strategy I Fe uptake system respond to Fe deficiency at mildly acidic and alkaline pH by measuring root ferric chelate reductase (FCR) activity and expression of selected Fe uptake genes and riboflavin synthesis genes. Alkaline pH increased cucumber (Cucumis sativus L.) root FCR activity at full Fe supply, but alkaline stress abolished FCR response to low Fe supply. Alkaline pH or low Fe supply resulted in increased expression of Fe uptake genes, but riboflavin synthesis genes responded to Fe deficiency but not alkalinity. Iron deficiency increased expression of some common genes in roots and leaves, but alkaline stress blocked up-regulation of these genes in Fe-deficient leaves. In roots of the melon (Cucumis melo L.) fefe mutant, in which Fe uptake responses are blocked upstream of Fe uptake genes, alkaline stress or Fe deficiency up-regulation of certain Fe uptake and riboflavin synthesis genes was inhibited, indicating a central role for the FeFe protein. These results suggest a model implicating shoot-to-root signaling of Fe status to induce Fe uptake gene expression in roots

Alkaline stress and iron deficiency regulate iron uptake and riboflavin synthesis gene expression differently in root and leaf tissue: implications for iron deficiency chlorosis

Iron (Fe) is an essential mineral that has low solubility in alkaline soils, where its deficiency results in chlorosis. Whether low Fe supply and alkaline pH stress are equivalent is unclear, as they have not been treated as separate variables in molecular physiological studies. Additionally, molecular responses to these stresses have not been studied in leaf and root tissues simultaneously. We tested how plants with the Strategy I Fe uptake system respond to Fe deficiency at mildly acidic and alkaline pH by measuring root ferric chelate reductase (FCR) activity and expression of selected Fe uptake genes and riboflavin synthesis genes. Alkaline pH increased cucumber (Cucumis sativus L.) root FCR activity at full Fe supply, but alkaline stress abolished FCR response to low Fe supply. Alkaline pH or low Fe supply resulted in increased expression of Fe uptake genes, but riboflavin synthesis genes responded to Fe deficiency but not alkalinity. Iron deficiency increased expression of some common genes in roots and leaves, but alkaline stress blocked up-regulation of these genes in Fe-deficient leaves. In roots of the melon (Cucumis melo L.) fefe mutant, in which Fe uptake responses are blocked upstream of Fe uptake genes, alkaline stress or Fe deficiency up-regulation of certain Fe uptake and riboflavin synthesis genes was inhibited, indicating a central role for the FeFe protein. These results suggest a model implicating shoot-to-root signaling of Fe status to induce Fe uptake gene expression in roots

Gene Expression Profiling of Iron Deficiency Chlorosis Sensitive and Tolerant Soybean Indicates Key Roles for Phenylpropanoids under Alkalinity Stress

Alkaline soils comprise 30% of the earth and have low plant-available iron (Fe) concentration, and can cause iron deficiency chlorosis (IDC). IDC causes soybean yield losses of $260 million annually. However, it is not known whether molecular responses to IDC are equivalent to responses to low iron supply. IDC tolerant and sensitive soybean lines provide a contrast to identify specific factors associated with IDC.We used RNA-seq to compare gene expression under combinations of normal pH (5.7) or alkaline pH (7.7, imposed by 2.5mM bicarbonate, or pH 8.2 imposed by 5mM bicarbonate) and normal (25μM) or low (1μM) iron conditions from roots of these lines. Thus, we were able to treat pH and Fe supply as separate variables. We also noted differential gene expression between IDC sensitive and tolerant genotypes in each condition. Classical iron uptake genes, including ferric-chelate reductase (FCR) and ferrous transporters, were upregulated by both Fe deficiency and alkaline stress, however, their gene products did not function well at alkaline pH. In addition, genes in the phenylpropanoid synthesis pathway were upregulated in both alkaline and low Fe conditions. These genes lead to the production of fluorescent root exudate (FluRE) compounds, such as coumarins. Fluorescence of nutrient solution increased with alkaline treatment, and was higher in the IDC tolerant line. Some of these genes also localized to previously identified QTL regions associated with IDC. We hypothesize that FluRE become essential at alkaline pH where the classical iron uptake system does not function well. This work could result in new strategies to screen for IDC tolerance, and provide breeding targets to improve crop alkaline stress tolerance

Transcriptomic and physiological characterization of the \u3ci\u3efefe\u3c/i\u3e mutant of melon (\u3ci\u3eCucumis melo\u3c/i\u3e) reveals new aspects of iron-copper crosstalk

Iron (Fe) and copper (Cu) homeostasis are tightly linked across biology. In previous work, Fe deficiency interacted with Cu-regulated genes and stimulated Cu accumulation. The C940-fe (fefe) Fe-uptake mutant of melon (Cucumis melo) was characterized, and the fefe mutant was used to test whether Cu deficiency could stimulate Fe uptake. Wild-type and fefe mutant transcriptomes were determined by RNA-seq under Fe and Cu deficiency. FeFe-regulated genes included core Fe uptake, metal homeostasis, and transcription factor genes. Numerous genes were regulated by both Fe and Cu. The fefe mutant was rescued by high Fe or by Cu deficiency, which stimulated ferric-chelate reductase activity, FRO2 expression, and Fe accumulation. Accumulation of Fe in Cu-deficient plants was independent of the normal Fe-uptake system. One of the four FRO genes in the melon and cucumber (Cucumis sativus) genomes was Fe-regulated, and one was Cu-regulated. Simultaneous Fe and Cu deficiency synergistically up-regulated Fe-uptake gene expression. Overlap in Fe and Cu deficiency transcriptomes highlights the importance of Fe-Cu crosstalk in metal homeostasis. The fefe gene is not orthologous to FIT, and thus identification of this gene will provide clues to help understand regulation of Fe uptake in plants

Characterization of FRO\u3csub\u3e1\u3c/sub\u3e, a Pea Ferric-Chelate Reductase Involved in Root Iron Acquisition

To acquire iron, many plant species reduce soil Fe(III) to Fe(II) by Fe(III)-chelate reductases embedded in the plasma membrane of root epidermal cells. The reduced product is then taken up by Fe(II) transporter proteins. These activities are induced under Fe deficiency. We describe here the FRO1 gene from pea (Pisum sativum), which encodes an Fe(III)-chelate reductase. Consistent with this proposed role, FRO1 shows similarity to other oxidoreductase proteins, and expression of FRO1 in yeast conferred increased Fe(III)-chelate reductase activity. Furthermore, FRO1 mRNA levels in plants correlated with Fe(III)-chelate reductase activity. Sites of FRO1 expression in roots, leaves, and nodules were determined. FRO1 mRNA was detected throughout the root, but was most abundant in the outer epidermal cells. Expression was detected in mesophyll cells in leaves. In root nodules, mRNA was detected in the infection zone and nitrogen-fixing region. These results indicate that FRO1 acts in root Fe uptake and they suggest a role in Fe distribution throughout the plant. Characterization of FRO1 has also provided new insights into the regulation of Fe uptake. FRO1 expression and reductase activity was detected only in Fe-deficient roots of Sparkle, whereas both were constitutive in brz and dgl, two mutants with incorrectly regulated Fe accumulation. In contrast, FRO1 expression was responsive to Fe status in shoots of all three plant lines. These results indicate differential regulation of FRO1 in roots and shoots, and improper FRO1 regulation in response to a shoot-derived signal of iron status in the roots of the brz and dgl mutants

Identification of new QTLs for seed mineral, cysteine, and methionine concentrations in soybean [Glycine max (L.) Merr.]

Increased concentrations of important nutrients in edible parts of plants could result in biofortified foods. Soybean [Glycine max (L.) Merr.] is a major legume crop and an important source of certain nutrients, including protein and minerals, in human and animal diets. Understanding the underlying genetic basis of seed composition is crucial to improving seed nutrient composition. In this study we used three soybean recombinant inbred line mapping populations derived from the crosses Williams 82 × DSR-173, Williams 82 × NKS19-90 and Williams 82 × Vinton 81, and constructed a joint linkage map from these populations. Forty quantitative trait loci (QTLs) were detected for 18 traits: seed weight, seed magnesium, sulfur, calcium, manganese, potassium, iron, cobalt, nickel, copper, zinc, selenium, molybdenum, cadmium and arsenic concentrations, total nitrogen:total sulfur (N:S) ratio, cysteine, and methionine concentrations. Using the joint linkage map, we detected nine QTLs that were not identified in the individual populations. We identified several candidate genes that might contribute to these traits, including transporters and genes involved in nitrogen and amino acid metabolism. Some strong QTLs had no obvious candidate genes, offering the possibility that subsequent confirmation of these QTLs may result in identification of new genes affecting seed nutrients in soybean. Seed weight and seed mineral concentrations were not highly correlated, suggesting the possibility of improving seed mineral concentrations without significant changes in seed weight. An inverse relationship between N:S ratio and most other minerals suggests the possibility of using N:S ratio as an indirect measure of seed mineral concentration in soybean breeding programs