Identification of a root-specific glycosyltransferase from Arabidopsis and characterization of its promoter

A set of Ds-element enhancer trap lines of Arabidopsis thaliana was generated and screened for expression patterns leading to the identification of a line that showed root-specific expression of the bacterial uidA reporter gene encoding β-glucuronidase (GUS). The insertion of the Ds element was found to be immediately downstream to a glycosyltransferase gene At1g73160. Analysis of At1g73160 expression showed that it is highly root-specific. Isolation and characterization of the upstream region of the At1g73160 gene led to the definition of a 218 bp fragment that is sufficient to confer root-specific expression. Sequence analysis revealed that several regulatory elements were implicated in expression in root tissue. The promoter identified and characterized in this study has the potential to be applied in crop biotechnology for directing the root-specific expression of transgenes

The Arabidopsis-mei2-Like Genes Play a Role in Meiosis and Vegetative Growth in Arabidopsis

The Arabidopsis-mei2-Like (AML) genes comprise a five-member gene family related to the mei2 gene, which is a master regulator of meiosis in Schizosaccharomyces pombe and encodes an RNA binding protein. We have analyzed the AML genes to assess their role in plant meiosis and development. All five AML genes were expressed in both vegetative and reproductive tissues. Analysis of AML1-AML5 expression at the cellular level indicated a closely similar expression pattern. In the inflorescence, expression was concentrated in the shoot apical meristem, young buds, and reproductive organ primordia. Within the reproductive organs, strong expression was observed in meiocytes and developing gametes. Functional analysis using RNA interference (RNAi) and combinations of insertion alleles revealed a role for the AML genes in meiosis, with RNAi lines and specific multiple mutant combinations displaying sterility and a range of defects in meiotic chromosome behavior. Defects in seedling growth were also observed at low penetrance. These results indicate that the AML genes play a role in meiosis as well as in vegetative growth and reveal conservation in the genetic mechanisms controlling meiosis in yeast and plants

The DUET gene is necessary for chromosome organization and progression during male meiosis in Arabidopsis and encodes a PHD finger protein

Progression through the meiotic cell cycle is an essential part of the developmental program of sporogenesis in plants. The duet mutant of Arabidopsis was identified as a male sterile mutant that lacked pollen and underwent an aberrant male meiosis. Male meiocyte division resulted in the formation of two cells instead of a normal tetrad. In wild type, male meiosis extends across two successive bud positions in an inflorescence whereas in duet, meiotic stages covered three to five bud positions indicating defective progression. Normal microspores were absent in the mutant and the products of the aberrant meiosis were uni- to tri-nucleate cells that later degenerated, resulting in anthers containing largely empty locules. Defects in male meiotic chromosome organization were observed starting from diplotene and extending to subsequent stages of meiosis. There was an accumulation of meiotic structures at metaphase 1, suggesting an arrest in cell cycle progression. Double mutant analysis revealed interaction with dyad, a mutation causing chromosome cohesion during female meiosis. Cloning and molecular analysis of DUET indicated that it potentially encodes a PHD-finger protein and shows specific expression in male meiocytes. Taken together these data suggest that DUET is required for male meiotic chromosome organization and progression

Perturbation of Arabidopsis Amino Acid Metabolism Causes Incompatibility with the Adapted Biotrophic Pathogen Hyaloperonospora arabidopsidis[C][W][OA]

This work identified two different Arabidopsis mutants that have reduced susceptibility to an infectious biotrophic pathogen due to overaccumulation of the amino acid Thr. This is detrimental for the host plant and the infecting pathogen but does not affect disease caused by some other pathogen species. Therefore, the host metabolic state can influence disease in quite a specific manner

Structural and Functional Significance of the N- and C‑Terminal Appendages in <i>Arabidopsis</i> Truncated Hemoglobin

Plant hemoglobins constitute three distinct groups: symbiotic, nonsymbiotic, and truncated hemoglobins. Structural investigation of symbiotic and nonsymbiotic (class I) hemoglobins revealed the presence of a vertebrate-like 3/3 globin fold in these proteins. In contrast, plant truncated hemoglobins are similar to bacterial truncated hemoglobins with a putative 2/2 α-helical globin fold. While multiple structures have been reported for plant hemoglobins of the first two categories, for plant truncated globins only one structure has been reported of late. Here, we report yet another crystal structure of the truncated hemoglobin from <i>Arabidopsis thaliana</i> (AHb3) with two water molecules in the heme pocket, of which one is distinctly coordinated to the heme iron, unlike the only available crystal structure of AHb3 with a hydroxyl ligand. AHb3 was monomeric in its crystallographic asymmetric unit; however, dimer was evident in the crystallographic symmetry, and the globin indeed existed as a stable dimer in solution. The tertiary structure of the protein exhibited a bacterial-like 2/2 α-helical globin fold with an additional N-terminal α-helical extension and disordered C-termini. To address the role of these extended termini in AHb3, which is yet unknown, N- and C-terminal deletion mutants were created and characterized and molecular dynamics simulations performed. The C-terminal deletion had an insignificant effect on most properties but perturbed the dimeric equilibrium of AHb3 and significantly influenced azide binding kinetics in the ferric state. These results along with the disordered nature of the C-terminus indicated its putative role in intramolecular or intermolecular interactions probably regulating protein–ligand and protein–protein interactions. While the N-terminal deletion did not change the overall globin fold, stability, or ligand binding kinetics, it seemed to have influenced coordination at the heme iron, the hydration status of the active site, and the quaternary structure of AHb3. Evidence indicated that the N-terminus is the predominant factor regulating the quaternary interaction appropriate to physiological requirements, dynamics of the side chains in the heme pocket, and tunnel organization in the protein matrix