The \u3ci\u3epho1;2a\u27-m1.1\u3c/i\u3e allele of \u3ci\u3ePhosphate1\u3c/i\u3e conditions misregulation of the phosphorus starvation response in maize (\u3ci\u3eZea mays ssp. mays L.\u3c/i\u3e)

Plant PHO1 proteins play a central role in the translocation and sensing of inorganic phosphate. The maize (Zea mays ssp. mays) genome encodes two co-orthologs of the Arabidopsis PHO1 gene, designated ZmPho1;2a and ZmPho1;2b. Here, we report the characterization of the transposon footprint allele Zmpho1;2a\u27-m1.1, which we refer to hereafter as pho1;2a. The pho1;2a allele is a stable derivative formed by excision of an Activator transposable element from the ZmPho1;2a gene. The pho1;2a allele contains an 8-bp insertion at the point of transposon excision that disrupts the reading frame and is predicted to generate a premature translational stop. We show that the pho1;2a allele is linked to a dosage-dependent reduction in Pho1;2a transcript accumulation and a mild reduction in seedling growth. Characterization of shoot and root transcriptomes under full nutrient, low nitrogen, low phosphorus, and combined low nitrogen and low phosphorus conditions identified 1100 differentially expressed genes between wild-type plants and plants carrying the pho1;2a mutation. Of these 1100 genes, 966 were upregulated in plants carrying pho1;2a, indicating the wildtype PHO1;2a to predominantly impact negative gene regulation. Gene set enrichment analysis of the pho1;2a-misregulated genes revealed associations with phytohormone signaling and the phosphate starvation response. In roots, differential expression was broadly consistent across all nutrient conditions. In leaves, differential expression was largely specific to low phosphorus and combined low nitrogen and low phosphorus conditions. Of 276 genes upregulated in the leaves of pho1;2a mutants in the low phosphorus condition, 153 were themselves induced in wild-type plants with respect to the full nutrient condition. Our observations suggest that Pho1;2a functions in the fine-tuning of the transcriptional response to phosphate starvation through maintenance and/or sensing of plant phosphate status

Genome wide characterization of barley NAC transcription factors enables the identification of grain-specific transcription factors exclusive for the Poaceae family of monocotyledonous plants.

The plant NAC transcription factors depict one of the largest plant transcription factor families. They regulate a wide range of different developmental processes and most probably played an important role in the evolutionary diversification of plants. This makes comparative studies of the NAC transcription factor family between individual species and genera highly relevant and such studies have in recent years been greatly facilitated by the increasing number of fully sequenced complex plant genomes. This study combines the characterization of the NAC transcription factors in the recently sequenced genome of the cereal crop barley with expression analysis and a comprehensive phylogenetic characterization of the NAC transcription factors in other monocotyledonous plant species. Our results provide evidence for the emergence of a NAC transcription factor subclade that is exclusively expressed in the grains of the Poaceae family of grasses. These notably comprise a number of cereal crops other than barley, such as wheat, rice, maize or millet, which are all cultivated for their starchy edible grains. Apparently, the grain specific subclade emerged from a well described subgroup of NAC transcription factors associated with the senescence process. A promoter exchange subsequently resulted in grain specific expression. We propose to designate this transcription factor subclade Grain-NACs and we discuss their involvement in programmed cell death as well as their potential role in the evolution of the Poaceae grain, which doubtlessly is of central importance for human nutrition

The Phosphoglycerate Kinase (PGK) Gene Family of Maize (Zea mays var. B73)

Phosphoglycerate kinase (PGK, E.C. 2.7.2.3) interconverts ADP + 1,3-bisphospho-glycerate (1,3-bPGA) to ATP + 3-phosphoglycerate (3PGA). While most bacteria have a single pgk gene and mammals possess two copies, plant genomes contain three or more PGK genes. In this study, we identified five Pgk genes in the Zea mays var. B73 genome, predicted to encode proteins targeted to different subcellular compartments: ZmPgk1, ZmPgk2, and ZmPgk4 (chloroplast), ZmPgk3 (cytosol), and ZmPgk5 (nucleus). The expression of ZmPgk3 was highest in non-photosynthetic tissues (roots and cobs), where PGK activity was also greatest, consistent with a function in glycolysis. Green tissues (leaf blade and husk leaf) showed intermediate levels of PGK activity, and predominantly expressed ZmPgk1 and ZmPgk2, suggesting involvement in photosynthetic metabolism. ZmPgk5 was weakly expressed and ZmPgk4 was not detected in any tissue. Phylogenetic analysis showed that the photosynthetic and glycolytic isozymes of plants clustered together, but were distinct from PGKs of animals, fungi, protozoa, and bacteria, indicating that photosynthetic and glycolytic isozymes of plants diversified after the divergence of the plant lineage from other groups. These results show the distinct role of each PGK in maize and provide the basis for future studies into the regulation and function of this key enzyme

The pho1;2a′‐m1.1 allele of Phosphate1 conditions misregulation of the phosphorus starvation response in maize (Zea mays ssp. mays L.)

Abstract Plant PHO1 proteins play a central role in the translocation and sensing of inorganic phosphate. The maize (Zea mays ssp. mays) genome encodes two co‐orthologs of the Arabidopsis PHO1 gene, designated ZmPho1;2a and ZmPho1;2b. Here, we report the characterization of the transposon footprint allele Zmpho1;2a′‐m1.1, which we refer to hereafter as pho1;2a. The pho1;2a allele is a stable derivative formed by excision of an Activator transposable element from the ZmPho1;2a gene. The pho1;2a allele contains an 8‐bp insertion at the point of transposon excision that disrupts the reading frame and is predicted to generate a premature translational stop. We show that the pho1;2a allele is linked to a dosage‐dependent reduction in Pho1;2a transcript accumulation and a mild reduction in seedling growth. Characterization of shoot and root transcriptomes under full nutrient, low nitrogen, low phosphorus, and combined low nitrogen and low phosphorus conditions identified 1100 differentially expressed genes between wild‐type plants and plants carrying the pho1;2a mutation. Of these 1100 genes, 966 were upregulated in plants carrying pho1;2a, indicating the wild‐type PHO1;2a to predominantly impact negative gene regulation. Gene set enrichment analysis of the pho1;2a‐misregulated genes revealed associations with phytohormone signaling and the phosphate starvation response. In roots, differential expression was broadly consistent across all nutrient conditions. In leaves, differential expression was largely specific to low phosphorus and combined low nitrogen and low phosphorus conditions. Of 276 genes upregulated in the leaves of pho1;2a mutants in the low phosphorus condition, 153 were themselves induced in wild‐type plants with respect to the full nutrient condition. Our observations suggest that Pho1;2a functions in the fine‐tuning of the transcriptional response to phosphate starvation through maintenance and/or sensing of plant phosphate status

Overexpression of Grain Amaranth (<i>Amaranthus hypochondriacus</i>) AhERF or AhDOF Transcription Factors in <i>Arabidopsis thaliana</i> Increases Water Deficit- and Salt-Stress Tolerance, Respectively, via Contrasting Stress-Amelioration Mechanisms

<div><p>Two grain amaranth transcription factor (TF) genes were overexpressed in Arabidopsis plants. The first, coding for a group VII ethylene response factor TF (i.e., AhERF-VII) conferred tolerance to water-deficit stress (WS) in transgenic Arabidopsis without affecting vegetative or reproductive growth. A significantly lower water-loss rate in detached leaves coupled to a reduced stomatal opening in leaves of plants subjected to WS was associated with this trait. WS tolerance was also associated with an increased antioxidant enzyme activity and the accumulation of putative stress-related secondary metabolites. However, microarray and GO data did not indicate an obvious correlation between WS tolerance, stomatal closure, and abscisic acid (ABA)-related signaling. This scenario suggested that stomatal closure during WS in these plants involved ABA-independent mechanisms, possibly involving reactive oxygen species (ROS). WS tolerance may have also involved other protective processes, such as those employed for methyl glyoxal detoxification. The second, coding for a class A and cluster I DNA binding with one finger TF (i.e., AhDof-AI) provided salt-stress (SS) tolerance with no evident fitness penalties. The lack of an obvious development-related phenotype contrasted with microarray and GO data showing an enrichment of categories and genes related to developmental processes, particularly flowering. SS tolerance also correlated with increased superoxide dismutase activity but not with augmented stomatal closure. Additionally, microarray and GO data indicated that, contrary to AhERF-VII, SS tolerance conferred by AhDof-AI in Arabidopsis involved ABA-dependent and ABA-independent stress amelioration mechanisms.</p></div

Phylogenetic tree including the AhERF-VII of <i>A</i>. <i>hypochondriacus</i> together with all the <i>Arabidopsis thaliana</i> ERF proteins.

<p>Also shown are the highly homologous GbERF1 and GbERF2 proteins from <i>Gossipum barbadense</i>, and the GhERF protein from <i>G</i>. <i>hirsutum</i>. The phylogenetic tree was constructed using the neighbor joining method with amino acid sequence data. It was drawn using the TreeView program, based on alignments obtained using MUSCLE software. The bootstrap values shown are in percent.</p

The overexpression of <i>AhERF-VII</i> in Arabidopsis modifies its metabolic pattern in optimal growing conditions and in both water-deficit stress and recovery conditions.

<p>Metabolic heat map obtained from acidified methanol extracts obtained from leaves collected from wild type (WT) and OE-<i>AhERF-VII Arabidopsis</i> plants (line EL25) grown in optimal conditions (Op), or subjected to water stress for 6 d (WS), or allowed to recover from stress, 1 d after normal watering was reestablished (R). The 50 most abundant ionizable metabolites were selected to obtain the metabolic heat-map within a 80–1300 m/z range. The results shown are those obtained from a representative experiment that was repeated thrice with similar results.</p

Phylogenetic tree of the AhDOF-AI protein of <i>A</i>. <i>hypochondriacus</i> together with all Dof domain-containing proteins from soybean (<i>Glycine max</i>, GmDof), <i>Arabidopsis thaliana</i> (AtDof), and rice (<i>Oryza sativa</i>, OsDof).

<p>Also shown is a highly homologous Dof protein from <i>Beta vulgaris</i> (BvDof). The phylogenetic tree was constructed using the neighbor joining method with amino acid sequence data. It was drawn using the TreeView program, based on alignments obtained using MUSCLE software. The 1050 bootstrap values shown are in percent.</p

The overexpression of <i>AhDof-AI</i> in Arabidopsis modifies its metabolic pattern in optimal growing conditions and under acute salt stress conditions.

<p>Metabolic heat map obtained from acidified methanol extracts obtained from leaves collected from wild type (WT) and OE-<i>AhDof-AI Arabidopsis</i> plants (line DL2) grown in optimal conditions (Op), or subjected to acute salt stress for 3 d (SS). The 50 most abundant ionizable metabolites were selected to obtain the metabolic heat-map within a 80–1300 m/z range. The results shown are those obtained from a representative experiment that was repeated thrice with similar results.</p