Brd1 Gene in Maize Encodes a Brassinosteroid C-6 Oxidase

The role of brassinosteroids in plant growth and development has been well-characterized in a number of plant species. However, very little is known about the role of brassinosteroids in maize. Map-based cloning of a severe dwarf mutant in maize revealed a nonsense mutation in an ortholog of a brassinosteroid C-6 oxidase, termed brd1, the gene encoding the enzyme that catalyzes the final steps of brassinosteroid synthesis. Homozygous brd1–m1 maize plants have essentially no internode elongation and exhibit no etiolation response when germinated in the dark. These phenotypes could be rescued by exogenous application of brassinolide, confirming the molecular defect in the maize brd1-m1 mutant. The brd1-m1 mutant plants also display alterations in leaf and floral morphology. The meristem is not altered in size but there is evidence for differences in the cellular structure of several tissues. The isolation of a maize mutant defective in brassinosteroid synthesis will provide opportunities for the analysis of the role of brassinosteroids in this important crop system

Analysis of the Maize dicer-like1 Mutant, fuzzy tassel, Implicates MicroRNAs in Anther Maturation and Dehiscence

Sexual reproduction in plants requires development of haploid gametophytes from somatic tissues. Pollen is the male gametophyte and develops within the stamen; defects in the somatic tissues of the stamen and in the male gametophyte itself can result in male sterility. The maize fuzzy tassel (fzt) mutant has a mutation in dicer-like1 (dcl1), which encodes a key enzyme required for microRNA (miRNA) biogenesis. Many miRNAs are reduced in fzt, and fzt mutants exhibit a broad range of developmental defects, including male sterility. To gain further insight into the roles of miRNAs in maize stamen development, we conducted a detailed analysis of the male sterility defects in fzt mutants. Early development was normal in fzt mutant anthers, however fzt anthers arrested in late stages of anther maturation and did not dehisce. A minority of locules in fzt anthers also exhibited anther wall defects. At maturity, very little pollen in fzt anthers was viable or able to germinate. Normal pollen is tricellular at maturity; pollen from fzt anthers included a mixture of unicellular, bicellular, and tricellular pollen. Pollen from normal anthers is loaded with starch before dehiscence, however pollen from fzt anthers failed to accumulate starch. Our results indicate an absolute requirement for miRNAs in the final stages of anther and pollen maturation in maize. Anther wall defects also suggest that miRNAs have key roles earlier in anther development. We discuss candidate miRNAs and pathways that might underlie fzt anther defects, and also note that male sterility in fzt resembles water deficit-induced male sterility, highlighting a possible link between development and stress responses in plants.ECU Open Access Publishing Support Fun

The maize root stem cell niche: a partnership between two sister cell populations

Using transcript profile analysis, we explored the nature of the stem cell niche in roots of maize (Zea mays). Toward assessing a role for specific genes in the establishment and maintenance of the niche, we perturbed the niche and simultaneously monitored the spatial expression patterns of genes hypothesized as essential. Our results allow us to quantify and localize gene activities to specific portions of the niche: to the quiescent center (QC) or the proximal meristem (PM), or to both. The data point to molecular, biochemical and physiological processes associated with the specification and maintenance of the niche, and include reduced expression of metabolism-, redox- and certain cell cycle-associated transcripts in the QC, enrichment of auxin-associated transcripts within the entire niche, controls for the state of differentiation of QC cells, a role for cytokinins specifically in the PM portion of the niche, processes (repair machinery) for maintaining DNA integrity and a role for gene silencing in niche stabilization. To provide additional support for the hypothesized roles of the above-mentioned and other transcripts in niche specification, we overexpressed, in Arabidopsis, homologs of representative genes (eight) identified as highly enriched or reduced in the maize root QC. We conclude that the coordinated changes in expression of auxin-, redox-, cell cycle- and metabolism-associated genes suggest the linkage of gene networks at the level of transcription, thereby providing additional insights into events likely associated with root stem cell niche establishment and maintenance

The Bactofilin Cytoskeleton Protein BacM of Myxococcus xanthus Forms an Extended β-Sheet Structure Likely Mediated by Hydrophobic Interactions

Bactofilins are novel cytoskeleton proteins that are widespread in Gram-negative bacteria. Myxococcus xanthus, an important predatory soil bacterium, possesses four bactofilins of which one, BacM (Mxan_7475) plays an important role in cell shape maintenance. Electron and fluorescence light microscopy, as well as studies using over-expressed, purified BacM, indicate that this protein polymerizes in vivo and in vitro into ~3 nm wide filaments that further associate into higher ordered fibers of about 10 nm. Here we use a multipronged approach combining secondary structure determination, molecular modeling, biochemistry, and genetics to identify and characterize critical molecular elements that enable BacM to polymerize. Our results indicate that the bactofilin-determining domain DUF583 folds into an extended β-sheet structure, and we hypothesize a left-handed β-helix with polymerization into 3 nm filaments primarily via patches of hydrophobic amino acid residues. These patches form the interface allowing head-to-tail polymerization during filament formation. Biochemical analyses of these processes show that folding and polymerization occur across a wide variety of conditions and even in the presence of chaotropic agents such as one molar urea. Together, these data suggest that bactofilins are comprised of a structure unique to cytoskeleton proteins, which enables robust polymerization

Flower palate ultrastructure of the carnivorous plant Genlisea hispidula Stapf with remarks on the structure and function of the palate in the subgenus Genlisea (Lentibulariaceae)

In the genus Genlisea as well as in its sister genus Utricularia, the palate probably plays a key role in providing the colour, mechanical and olfactory stimuli to attract insect pollinators and to guide them to the generative structures and the nectary spur. However, information about the micro-morphology of the palate of Genlisea is scarce. This study aims to examine the structure of the palate in Genlisea hispidula in detail as well as the palate from other five species from the subgenus Genlisea. In particular, its aim is to ascertain whether these palates function as an area for the osmophores in the flower or whether they produce nectar. We showed that the palate in all of the species that were examined was the glandular type and that it had capitate, glandular trichomes, which had a similar general architecture across the species that were examined. No nectar secretion was observed on the palates. The ultrastructure of the palate trichomes showed that the palate glandular trichomes most probably function as scent glands that produce an olfactory stimulus for flower pollinators

Transcription factor ANAC032 modulates JA/SA signalling in response to Pseudomonas syringae

Responses to pathogens, including host transcriptional reprogramming, require partially antagonistic signalling pathways dependent on the phytohormones salicylic (SA) and jasmonic (JA) acids. However, upstream factors modulating the interplay of these pathways are not well characterized. Here, we identify the transcription factor ANAC032 from Arabidopsis thaliana as one such regulator in response to the bacterial pathogen Pseudomonas syringae pv. tomato DC3000 (Pst). ANAC032 directly represses MYC2 activation upon Pst attack, resulting in blockage of coronatine‐mediated stomatal reopening which restricts entry of bacteria into plant tissue. Furthermore, ANAC032 activates SA signalling by repressing NIMIN1, a key negative regulator of SA‐dependent defence. Finally, ANAC032 reduces expression of JA‐responsive genes, including PDF1.2A. Thus, ANAC032 enhances resistance to Pst by generating an orchestrated transcriptional output towards key SA‐ and JA‐signalling genes coordinated through direct binding of ANAC032 to the MYC2, NIMIN1 and PDF1.2A promoters