Search

Cytokinin plays an important role in plant stress responses via a multistep signaling pathway, involving the histidine phosphotransfer proteins (HPs). In Arabidopsis thaliana, the AHP2, AHP3 and AHP5 proteins are known to affect drought responses; however, the role of AHP4 in drought adaptation remains undetermined. In the present study, using a loss-of-function approach we showed that AHP4 possesses an important role in the response of Arabidopsis to drought. This is evidenced by the higher survival rates of ahp4 than wild-type (WT) plants under drought conditions, which is accompanied by the downregulated AHP4 expression in WT during periods of dehydration. Comparative transcriptome analysis of ahp4 and WT plants revealed AHP4-mediated expression of several dehydration- and/or abscisic acid-responsive genes involved in modulation of various physiological and biochemical processes important for plant drought acclimation. In comparison with WT, ahp4 plants showed increased wax crystal accumulation in stems, thicker cuticles in leaves, greater sensitivity to exogenous abscisic acid at germination, narrow stomatal apertures, heightened leaf temperatures during dehydration, and longer root length under osmotic stress. In addition, ahp4 plants showed greater photosynthetic efficiency, lower levels of reactive oxygen species, reduced electrolyte leakage and lipid peroxidation, and increased anthocyanin contents under drought, when compared with WT. These differences displayed in ahp4 plants are likely due to upregulation of genes that encode enzymes involved in reactive oxygen species scavenging and non-enzymatic antioxidant metabolism. Overall, our findings suggest that AHP4 plays a crucial role in plant drought adaptation.

Land plant spermatozoids commonly possess characteristic structures such as the spline, which consists of a microtubule array, the multilayered structure (MLS) in which the uppermost layer is a continuum of the spline, and multiple flagella. However, the molecular mechanisms underpinning spermatogenesis remain to be elucidated. We successfully identified candidate genes involved in spermatogenesis, deeply divergent BLD10s, by computational analyses combining multiple methods and omics data. We then examined the functions of BLD10s in the liverwort Marchantia polymorpha and the moss Physcomitrium patens. MpBLD10 and PpBLD10 are required for normal basal body (BB) and flagella formation. Mpbld10 mutants exhibited defects in remodeling of the cytoplasm and nucleus during spermatozoid formation, and thus MpBLD10 should be involved in chromatin reorganization and elimination of the cytoplasm during spermiogenesis. We identified orthologs of MpBLD10 and PpBLD10 in diverse Streptophyta and found that MpBLD10 and PpBLD10 are orthologous to BLD10/CEP135 family proteins, which function in BB assembly. However, BLD10s evolved especially quickly in land plants and MpBLD10 might have acquired additional functions in spermatozoid formation through rapid molecular evolution.

Over-expression of sigE, a gene encoding an RNA polymerase sigma factor in the unicellular cyanobacterium Synechocystis sp. PCC 6803, is known to activate sugar catabolism and bioplastic production. In this study, we investigated the effects of sigE over-expression on cell morphology, photosynthesis and hydrogen production in this cyanobacterium. Transmission electron and scanning probe microscopic analyses revealed that sigE over-expression increased the cell size, possibly as a result of aberrant cell division. Over-expression of sigE reduced respiration and photosynthesis activities via changes in gene expression and chlorophyll fluorescence. Hydrogen production under micro-oxic conditions is enhanced in sigE over-expressing cells. Despite these pleiotropic phenotypes, the sigE over-expressing strain showed normal cell viability under both nitrogen-replete and nitrogen-depleted conditions. These results provide insights into the inter-relationship among metabolism, cell morphology, photosynthesis and hydrogen production in this unicellular cyanobacterium.

SUMMARY Mitochondria and plastids multiply by division in eukaryotic cells. Recently, the eukaryotic homolog of the bacterial cell division protein FtsZ was identified and shown to play an important role in the organelle division process inside the inner membrane. To explore the evolution of FtsZ proteins, and to accumulate data on the protein import system in mitochondria and plastids of the red algal lineage, one mitochondrial and three plastid ftsZ genes were isolated from the diatom Chaetoceros neogracile, whose plastids were acquired by secondary endosymbiotic uptake of a red alga. Protein import into organelles depends on the N-terminal organelle targeting sequences. N-terminal bipartite presequences consisting of an endoplasmic reticulum signal peptide and a plastid transit peptide are required for protein import into diatom plastids. To characterize the organelle targeting peptides of C. neogracile, we observed the localization of each green fluorescent protein-tagged predicted organelle targeting peptide in cultured tobacco cells and diatom cells. Our data suggested that each targeting sequences functioned both in tobacco cultured cells and diatom cells.

SUMMARYCtBP/BARS is a unique protein family in having quite diversified cellular functions, intercellular localizations,and developmental roles. ANGUSTIFOLIA (AN) is the sole homolog of CtBP/BARS from Arabidopsis thaliana,although it has plant AN-specific motifs and a long C-terminus. Previous studies suggested that AN wouldfunction in the nucleus as a transcriptional co-repressor, as CtBPs function in animals; however, preciseverification has been lacking. In this paper, we isolated a homologous gene (MAN)ofAN from liverwort,Marchantia polymorpha. Transformation of the Arabidopsis an-1 mutant with 35S-driven MAN completelycomplemented the an-1 phenotype, although it lacks the putative nuclear localization signal (NLS) that existsinANproteinsisolatedfromother plantspecies.WeconstructedseveralplasmidsforexpressingmodifiedANswith amino acid substitutions in known motifs. The results clearly indicated that modified AN with mutationsin the putative NLS-like domain could complement the an-1 phenotype. Therefore, we re-examinedlocalization of AN using several techniques. Our results demonstrated that AN localizes on punctuatestructures around the Golgi, partially overlapping with a trans-Golgi network resident, which highlighted anunexpected link between leaf development and membrane trafficking. We should reconsider the roles andevolutionary traits of AN based on these findings.Keywords: ANGUSTIFOLIA, CtBP/BARS, Golgi, Marchantia polymorpha, TGN.INTRODUCTIONLeaf development is divided into two processes, cell prolif-eration and cell differentiation. In the cell differentiationprocess, genetic pathways controlling leaf cell shape havebeen revealed by the characterization of two mutants ofArabidopsis thaliana (hereafter Arabidopsis): angustifolia(an) and rotundifolia3 (rot3). The an mutant was originallyisolated by Re´dei (1962) as a mutant having a narrow leafand twisted fruit. Later studies reported that an has tric-homes with two branches (Hu¨lskampet al., 1994) and its leafcells are narrower and thicker than wild-type cells (Tsukayaet al., 1994; Tsuge et al., 1996). In contrast, rot3 has short,rounded leaves resulting from reduced cell expansion alongthe leaf length direction (Tsuge et al., 1996). These axis-specific defects in cell expansion demonstrate two inde-pendent polarity-dependent cell expansion systems (Tsugeet al., 1996; Tsukaya, 2002).

Phagocytosis is a fundamental cellular event for the uptake of nutrients from the environment in several kinds of eukaryote. Most ciliates egest waste and undigested materials in food vacuoles (FVs) through a cytoproct, which is a specific organelle for defecation. It is considered that FV egestion is initiated by fusion between the FV membrane and plasma membrane in a cytoproct and completed with retrieval of the membrane into a cytoplasmic space. In addition, electron microscopy indicated that microfilaments might be involved in the recycling process of the FV membrane in ciliates over 30 years ago; however, there is no conclusive evidence. Here we demonstrated actin organization on FV near a cytoproct in Tetrahymena thermophila by using a marker for a cytoproct. Moreover, it was revealed that cells treated with actin cytoskeletal inhibitor, Latrunculin B, might be suppressed for membrane retrieval in a cytoproct following FV egestion. On the other hand, the actin structures, likely to be the site of membrane retrieval, were frequently observed in the cells treated with cytoplasmic microtubules inhibitor, Nocodazole. We concluded that actin filaments were probably required for recycling of the FV membrane in a cytoproct although the role was not essential for FV egestion. In addition, it was possible that microtubules might be involved in transportation of recycling vesicles of FV coated with F-actin.

SUMMARY Plastids of glaucocystophytes are termed cyanelles and retain primitive features, such as a peptidoglycan wall. We isolated a full-length prokaryotic plastid division gene, FtsZ, from the glaucocystophyte alga Cyanophora paradoxa Korshikov (CpFtsZ-cy). CpftsZ-cy has a chloroplast-targeting signal at the N-teminus. Immunofluorescence microscopy showed that CpFtsZ-cy forms a ring-like structure at the division plane of cyanelles.