The homeologous Zea mays gigantea genes: characterization of expression and novel mutant alleles

The two homeologous Zea mays gigantea (gi) genes, gi1 and gi2, arose from the last genome duplication event in the maize lineage. Homologs of these genes in other species are required for correct circadian rhythms and proper regulation of growth and development. Here we characterized the expression of these two maize gi genes. Although gi1 and gi2 shared comparable 24-hour rhythmic expression profiles, gi1 levels were consistently higher than gi2. Furthermore, short day photoperiods repressed gi2 expression. The transcriptional unit for gi1 is established based on 5’-RACE analysis. Two independent mutant alleles for gi1 are described that are caused by transposons of the Mutator (Mu) class inserted into the 5’-end of the gene. The type of Mu element and position of the transposon in gi1 was different for each gi1 allele. Mutant plants had a marked reduction in gi1 expression and carried transcripts interrupted by the Mu element. Together, these results provide a deeper understanding of the gi genes in maize. In addition, the novel gi1 mutant alleles described here will be valuable tools to study gi1 function in maize, as well as the role of circadian clock regulation in maize metabolism, growth, and development

The maize brown midrib6 (bm6) mutation encodes a functional GTP Cyclohydrolase1

Brown midrib mutations in maize (Zea mays L.) and sorghum (Sorghum bicolor L.) alter lignin composition and enhance cell wall digestibility. These mutations are prime candidates for silage breeding. Six brown midrib mutants are currently known, brown midrib1 (bm1) to brown midrib6 (bm6). The bm1 and bm3 mutations are being used commercially for silage. The underlying genes responsible for five of the six bm mutations in maize (bm1, bm2, bm3, bm4, and bm5) are known. Chen and co-workers (2012) characterized the bm6 mutation, demonstratingthat bm6 increases cell wall digestibility and physically mapped bm6 within a 180 kilobase region on chromosome 2. The present investigation utilized map-based cloning to identify the candidate gene responsible for the bm6 phenotype as GTP Cyclohydrolase1 (GCH1) and validated the candidate gene through reverse genetics. Orthologs of bm6 include at least one paralogous gene in maize on chromosome 10 and various homologs in other grasses and dicots. The discovery that GCH1 is  responsible for the maize bm6 phenotype suggests that GCH1 plays a role in the tetrahydrofolate biosynthetic process

Roothairless5, which functions in maize (Zea mays L.) root hair initiation and elongation encodes a monocot-specific NADPH oxidase

Citation: Nestler, J., Liu, S., Wen, T. -., Paschold, A., Marcon, C., Tang, H. M., et al. (2014). Roothairless5, which functions in maize (zea mays L.) root hair initiation and elongation encodes a monocot-specific NADPH oxidase. Retrieved from krex.k-state.edu.Root hairs are instrumental for nutrient uptake in monocot cereals. The maize (Zea mays L.) roothairless5 (rth5) mutant displays defects in root hair initiation and elongation manifested by a reduced density and length of root hairs. Map-based cloning revealed that the rth5 gene encodes a monocot-specific NADPH oxidase. RNA-Seq, in situ hybridization and qRT-PCR experiments demonstrated that the rth5 gene displays preferential expression in root hairs but also accumulates to low levels in other tissues. Immunolocalization detected RTH5 proteins in the epidermis of the elongation and differentiation zone of primary roots. Because superoxide and hydrogen peroxide levels are reduced in the tips of growing rth5 mutant root hairs as compared to wild-type, and ROS is known to be involved in tip growth, we hypothesize that the RTH5 protein is responsible for establishing the high levels of ROS in the tips of growing root hairs required for elongation. Consistent with this hypothesis, a comparative RNA-Seq analysis of 6-day-old rth5 versus wild-type primary roots, revealed significant over-representation of only two gene ontology (GO) classes related to the biological functions (i.e., oxidation/reduction and carbohydrate metabolism) among 893 differentially expressed genes (FDR <5%). Within these two classes the subgroups “response to oxidative stress” and “cellulose biosynthesis” were most prominently represented

Identification and characterization of the maize arogenate dehydrogenase gene family

In plants, the amino acids tyrosine and phenylalanine are synthesized from arogenate by arogenate dehydrogenase and arogenate dehydratase, respectively, with the relative flux to each being tightly controlled. Here the characterization of a maize opaque endosperm mutant (mto140), which also shows retarded vegetative growth, is described The opaque phenotype co-segregates with a Mutator transposon insertion in an arogenate dehydrogenase gene (zmAroDH-1) and this led to the characterization of the four-member family of maize arogenate dehydrogenase genes (zmAroDH-1–zmAroDH-4) which share highly similar sequences. A Mutator insertion at an equivalent position in AroDH-3, the most closely related family member to AroDH-1, is also associated with opaque endosperm and stunted vegetative growth phenotypes. Overlapping but differential expression patterns as well as subtle mutant effects on the accumulation of tyrosine and phenylalanine in endosperm, embryo, and leaf tissues suggest that the functional redundancy of this gene family provides metabolic plasticity for the synthesis of these important amino acids. mto140/arodh-1 seeds shows a general reduction in zein storage protein accumulation and an elevated lysine phenotype typical of other opaque endosperm mutants, but it is distinct because it does not result from quantitative or qualitative defects in the accumulation of specific zeins but rather from a disruption in amino acid biosynthesis

The dicer-like1 Homolog fuzzy tassel Is Required for the Regulation of Meristem Determinacy in the Inflorescence and Vegetative Growth in Maize

Plant architecture is determined by meristems that initiate leaves during vegetative development and flowers during reproductive development. Maize (Zea mays) inflorescences are patterned by a series of branching events, culminating in floral meristems that produce sexual organs. The maize fuzzy tassel (fzt) mutant has striking inflorescence defects with indeterminate meristems, fasciation, and alterations in sex determination. fzt plants have dramatically reduced plant height and shorter, narrower leaves with leaf polarity and phase change defects. We positionally cloned fzt and discovered that it contains a mutation in a dicer-like1 homolog, a key enzyme required for microRNA (miRNA) biogenesis. miRNAs are small noncoding RNAs that reduce target mRNA levels and are key regulators of plant development and physiology. Small RNA sequencing analysis showed that most miRNAs are moderately reduced in fzt plants and a few miRNAs are dramatically reduced. Some aspects of the fzt phenotype can be explained by reduced levels of known miRNAs, including miRNAs that influence meristem determinacy, phase change, and leaf polarity. miRNAs responsible for other aspects of the fzt phenotype are unknown and likely to be those miRNAs most severely reduced in fzt mutants. The fzt mutation provides a tool to link specific miRNAs and targets to discrete phenotypes and developmental roles.ECU Open Access Publishing Support Fun

Signaling from maize organ primordia via FASCIATED EAR3 regulates stem cell proliferation and yield traits.

Shoot apical meristems are stem cell niches that balance proliferation with the incorporation of daughter cells into organ primordia. This balance is maintained by CLAVATA-WUSCHEL feedback signaling between the stem cells at the tip of the meristem and the underlying organizing center. Signals that provide feedback from organ primordia to control the stem cell niche in plants have also been hypothesized, but their identities are unknown. Here we report FASCIATED EAR3 (FEA3), a leucine-rich-repeat receptor that functions in stem cell control and responds to a CLAVATA3/ESR-related (CLE) peptide expressed in organ primordia. We modeled our results to propose a regulatory system that transmits signals from differentiating cells in organ primordia back to the stem cell niche and that appears to function broadly in the plant kingdom. Furthermore, we demonstrate an application of this new signaling feedback, by showing that weak alleles of fea3 enhance hybrid maize yield traits.The fea3-0 allele was kindly provided by Victor Shcherbak, Krasnodar Res. Inst. Agric., Russia. We acknowledge funding from a collaborative agreement with Dupont Pioneer, and from NSF Plant Genome Research Program grant # IOS-1238202 and MCB-1027445, and with the support of the Gatsby Charitable Foundation (GAT3395/PR4) and Swedish Research Council (VR2013-4632) to HJ, and "Next-Generation BioGreen 21 Program (SSAC, Project No. PJ01137901)" Rural Development Administration, Republic of Korea. We also thank Ulises Hernandez for assistance with cloning, Amandine Masson for assistance with peptide assays, and members of the Jackson lab for comments on the manuscript.This is the author accepted manuscript. It is currently under an indefinite embargo pending publication by Nature Publishing Group