Functional characterization of duplicated B-class MADS-box genes in Japanese gentian

Key message

The heterodimer formation between B-class MADS-box proteins of GsAP3a and GsPI2 proteins plays a core role for petal formation in Japanese gentian plants.

Abstract

We previously isolated six B-class MADS-box genes (GsAP3a, GsAP3b, GsTM6, GsPI1, GsPI2, and GsPI3) from Japanese gentian (Gentiana scabra). To study the roles of these MADS-box genes in determining floral organ identities, we investigated protein–protein interactions among them and produced transgenic Arabidopsis and gentian plants overexpressing GsPI2 alone or in combination with GsAP3a or GsTM6. Yeast two-hybrid and bimolecular fluorescence complementation analyses revealed that among the GsPI proteins, GsPI2 interacted with both GsAP3a and GsTM6, and that these heterodimers were localized to the nuclei. The heterologous expression of GsPI2 partially converted sepals into petaloid organs in transgenic Arabidopsis, and this petaloid conversion phenomenon was accelerated by combined expression with GsAP3a but not with GsTM6. In contrast, there were no differences in morphology between vector-control plants and transgenic Arabidopsis plants expressing GsAP3a or GsTM6 alone. Transgenic gentian ectopically expressing GsPI2 produced an elongated tubular structure that consisted of an elongated petaloid organ in the first whorl and stunted inner floral organs. These results imply that the heterodimer formation between GsPI2 and GsAP3a plays a core role in determining petal and stamen identities in Japanese gentian, but other B-function genes might be important for the complete development of petal organs.

     

Segregative cell division and the cytoskeleton in two species of the genus Struvea (Cladophorales,Ulvophyceae, Chlorophyta)

The detailed segregative cell division (SCD) processes and changes in the arrangement of cortical microtubules and actin filaments were examined in two species of Struvea. SCD was initiated by the appearance of annular constrictions along the lateral side of a mother cell. The constrictions decreased in diameter, became thin, tubular in shape, and pinched the protoplasm of the mother cell into several protoplasmic sections. The protoplasmic sections expanded and developed into daughter cells, which appressed each other, and were arranged in a single row. Lateral branches protruded from the upper parts of the daughter cells. The protoplasm of the lateral branches was divided by secondary SCDs and was distributed amongst the new daughter cells. SCD and lateral branch formation were essential for morphogenesis in Struvea. Cortical microtubules were arranged parallel and longitudinally to the cell axis before SCD. When SCD was initiated, there was considerable undulation of the cortical microtubules and several transverse bundles appeared in the cytoplasmic zone where annular constrictions occurred. A microtubule‐disrupting drug (amiprophos methyl) inhibited SCD. Actin filaments maintained reticulate patterns before and during SCD. These results demonstrated that SCD in Struvea species was quite distinct from that in Dictyosphaeria cavernosa reported previously.     

An NMR analysis of ubiquitin recognition by yeast ubiquitin hydrolase: evidence for novel substrate recognition by a cysteine protease.

Yeast ubiquitin hydrolase 1 (YUH1), a cysteine protease that catalyzes the removal of ubiquitin C-terminal adducts, is important for the generation of monomeric ubiquitin. Heteronuclear NMR spectroscopy has been utilized to map the YUH1 binding surface on ubiquitin. When YUH1 was titrated into a sample of ubiquitin, approximately 50% of the (1)H-(15)N correlation peaks of ubiquitin were affected to some degree, as a result of binding to YUH1. It is noteworthy that the amide resonances of the basic residues (Arg42, Lys48, Arg72, and Lys74) were highly perturbed. These positively charged basic residues may be involved in direct interactions with the negatively charged acidic residues on YUH1. In addition to the electrostatic surface, the hydrophobic surfaces on ubiquitin (Leu8, Ile44, Phe45, Val70, Leu71, and Leu73) and YUH1 are also likely to contribute to the binding interaction. Furthermore, the amide resonances of Ile13, Leu43, Leu50, and Leu69, the side chains of which are not on the surface, were also highly perturbed, indicating substrate-induced changes in the environments of these residues as well. These large changes, observed from residues located throughout the five-stranded beta-sheet surface and the C-terminus, suggest that substrate recognition by YUH1 involves a wider area on ubiquitin.     

The N-glycolyl form of mouse sialyl Lewis X is recognized by selectins but not by HECA-452 and FH6 antibodies that were raised against human cells

E-, P- and L-selectins critically function in lymphocyte recirculation and recruiting leukocytes to inflammatory sites. MECA-79 antibody inhibits L-selectin-mediated lymphocyte adhesion in several species and does not require sialic acid in its epitope. Many other antibodies, however, recognize human selectin ligands expressing N-acetylneuraminic acid but not mouse selectin ligands expressing N-glycolylneuraminic acid, suggesting that difference in sialic acid in sialyl Lewis X leads to differential reactivity. We found that HECA-452 and FH6 monoclonal antibodies bind Chinese hamster ovary (CHO) cells expressing N-acetylneuraminyl Lewis X oligosaccharide but not its N-glycolyl form. Moreover, synthetic N-acetylneuraminyl Lewis X oligosaccharide but not its N-glycolyl oligosaccharide inhibited HECA-452 and FH6 binding. By contrast, E-, P- and L-selectin bound to CHO cells regardless of whether they express N-acetyl or N-glycolyl form of sialyl Lewis X, showing that selectins have a broader recognition capacity than HECA-452 and FH-6 anti-sialyl Lewis x antibodies. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Distribution and roles of X-family DNA polymerases in eukaryotes

Four types of DNA polymerase (Pol beta, Pol lambda, Pol mu and TdT) have been identified in eukaryotes as members of the polymerase X-family. Only vertebrates have all four types of enzyme. Plants and fungi have one or two X-family polymerases, while protostomes, such as fruit flies and nematodes, do not appear to have any. It is possible that the well-known metabolic pathways in which these enzymes are involved are restricted to the vertebrate world. The distribution of the DNA polymerases involved in DNA repair across the various biological kingdoms differs from that of the DNA polymerases involved in chromosomal DNA replication. In this review, we focus on the interesting pattern of distribution of the X-family enzymes across biological kingdoms and speculate on their roles.