Studies on the POLARIS gene of Arabidopsis

The POLARIS (PLS) gene of Arabidopsis encodes a 36 amino acid peptide required for correct root growth and vascular patterning. Previous work indicates that PLS acts as a negative regulator of ethylene signalling. The pls mutant has enhanced ethylene signalling, which is the key determinant of its short root phenotype and results in a ‘triple response’ phenotype when seedlings are grown in the dark in air. The defects can be rescued by inhibition of ethylene signalling but not by inhibitors of ethylene biosynthesis, and pls does not over-produce ethylene, indicating a role for the peptide in ethylene signalling. Inhibition of ethylene signalling either by genetic or pharmacological methods restores pls mutant root growth. These data implicate ethylene as an important regulator of root development and PLS is hypothesised as a component of an ethylene regulatory mechanism to modulate root growth. This work establishes a direct interaction between ETR1, an ethylene receptor protein, and PLS by using both Yeast Two Hybrid and Bimolecular Fluorescence Complementation assays. In addition, the pls mutant has defective auxin transport and accumulation. The present work shows that PLS is required for correct gravitropic response, gene expression in the quiescent centre and columella patterning (each mediated in part at least by auxin) and also for ACC-mediated auxin synthesis. It is therefore proposed that PLS has two principal roles in root growth and development. First, PLS may act as a negative regulator of the ethylene signalling pathway by interacting with ETR1. Second, PLS is required for ethylene-mediated auxin synthesis; evidence is presented that suggests that PLS acts downstream of WEI2, an enzyme required for ethylene-mediated auxin synthesis. These roles function independently to regulate correct auxin distribution and concentration in the root tip, to control root growth and development

MicroRNA and tasiRNA diversity in mature pollen of Arabidopsis thaliana

<p>Abstract</p> <p>Background</p> <p>New generation sequencing technology has allowed investigation of the small RNA populations of flowering plants at great depth. However, little is known about small RNAs in their reproductive cells, especially in post-meiotic cells of the gametophyte generation. Pollen - the male gametophyte - is the specialised haploid structure that generates and delivers the sperm cells to the female gametes at fertilisation. Whether development and differentiation of the male gametophyte depends on the action of microRNAs and trans-acting siRNAs guiding changes in gene expression is largely unknown. Here we have used 454 sequencing to survey the various small RNA populations present in mature pollen of <it>Arabidopsis thaliana</it>.</p> <p>Results</p> <p>In this study we detected the presence of 33 different microRNA families in mature pollen and validated the expression levels of 17 selected miRNAs by Q-RT-PCR. The majority of the selected miRNAs showed pollen-enriched expression compared with leaves. Furthermore, we report for the first time the presence of trans-acting siRNAs in pollen. In addition to describing new patterns of expression for known small RNAs in each of these classes, we identified 7 putative novel microRNAs. One of these, ath-MIR2939, targets a pollen-specific F-box transcript and we demonstrate cleavage of its target mRNA in mature pollen.</p> <p>Conclusions</p> <p>Despite the apparent simplicity of the male gametophyte, comprising just two different cell types, pollen not only utilises many miRNAs and trans-acting siRNAs expressed in the somatic tissues but also expresses novel miRNAs.</p

MSK-Mediated Phosphorylation of Histone H3 Ser28 Couples MAPK Signalling with Early Gene Induction and Cardiac Hypertrophy

Heart failure is a leading cause of death that develops subsequent to deleterious hypertrophic cardiac remodelling. MAPK pathways play a key role in coordinating the induction of gene expression during hypertrophy. Induction of the immediate early gene (IEG) response including activator protein 1 (AP-1) complex factors is a necessary and early event in this process. How MAPK and IEG expression are coupled during cardiac hypertrophy is not resolved. Here, in vitro, in rodent models and in human samples, we demonstrate that MAPK-stimulated IEG induction depends on the mitogen and stress-activated protein kinase (MSK) and its phosphorylation of histone H3 at serine 28 (pH3S28). pH3S28 in IEG promoters in turn recruits Brg1, a BAF60 ATP-dependent chromatin remodelling complex component, initiating gene expression. Without MSK activity and IEG induction, the hypertrophic response is suppressed. These studies provide new mechanistic insights into the role of MAPK pathways in signalling to the epigenome and regulation of gene expression during cardiac hypertrophy

Modelling and experimental analysis of hormonal crosstalk in Arabidopsis

An important question in plant biology is how genes influence the crosstalk between hormones to regulate growth. In this study, we model POLARIS (PLS) gene function and crosstalk between auxin, ethylene and cytokinin in Arabidopsis. Experimental evidence suggests that PLS acts on or close to the ethylene receptor ETR1, and a mathematical model describing possible PLS–ethylene pathway interactions is developed, and used to make quantitative predictions about PLS–hormone interactions. Modelling correctly predicts experimental results for the effect of the pls gene mutation on endogenous cytokinin concentration. Modelling also reveals a role for PLS in auxin biosynthesis in addition to a role in auxin transport. The model reproduces available mutants, and with new experimental data provides new insights into how PLS regulates auxin concentration, by controlling the relative contribution of auxin transport and biosynthesis and by integrating auxin, ethylene and cytokinin signalling. Modelling further reveals that a bell-shaped dose–response relationship between endogenous auxin and root length is established via PLS. This combined modelling and experimental analysis provides new insights into the integration of hormonal signals in plants

Development after isolation of <i>Botrytis deweyae</i> cultures from surface-sterilised <i>Hemerocallis</i> material.

<p>The initial development of multiple melanised sclerotia distributed across the colony surface can be seen in this maturing culture. Scale bar indicates 1</p

Phylogeny of <i>Botrytis</i> based on the combined analysis of 5 different genes.

<p>Sequences of <i>G3PDH</i>, <i>HSP60</i>, <i>RPB2</i>, <i>NEP1</i> and <i>NEP2</i> were used. The phylogenetic position of <i>B. deweyae</i> (B1 isolate, type) is underlined. The phylogeny was constructed using the genus <i>Sclerotinia</i> as the outgroup.</p