Danielle Vega

RNA-directed DNA methylation requires an AGO4-interacting member of the SPT5 elongation factor family

Recent studies have identified a conserved WG/GW‐containing motif, known as the Argonaute (AGO) hook, which is involved in the recruitment of AGOs to distinct components of the eukaryotic RNA silencing pathways. By using this motif as a model to detect new components in plant RNA silencing pathways, we identified SPT5‐like, a plant‐specific AGO4‐interacting member of the nuclear SPT5 (Suppressor of Ty insertion 5) RNA polymerase (RNAP) elongation factor family that is characterized by the presence of a carboxy‐terminal extension with more than 40 WG/GW motifs. Knockout SPT5‐like mutants show a decrease in the accumulation of several 24‐nt RNAs and hypomethylation at different loci revealing an implication in RNA‐directed DNA methylation (RdDM). Here, we propose that SPT5‐like emerged in plants as a facultative RNAP elongation factor. Its plant‐specific origin and role in RdDM might reflect functional interactions with plant‐specific RNA Pols required for RdDM.

Dimethylphthalate hydrolysis by specific microbial esterase

TWO BACTERIAL STRAINS: Arthrobacter sp. and Sphingomonas paucimobilis were isolated from soil by enrichment cultures using dimethylphthalate (DMP) or monomethylphthalate (MMP) as sole carbon source, respectively. DMP was rapidly transformed by an Arthrobacter sp. culture with formation of MMP and phthalic acid (PA) which is further degraded. This strain was unable to hydrolyse MMP. A mechanism of degradation of DMP was proposed with two ways: DMP-->PA and DMP-->MMP. The S. paucimobilis strain hydrolyses only MMP and a coculture of the two strains allowed a complete degradation of DMP.

PolV(PolIVb) function in RNA-directed DNA methylation requires the conserved active site and an additional plant-specific subunit

Two forms of a plant-specific RNA polymerase (Pol), PolIV(PolIVa) and PolV(PolIVb), currently defined by their respective largest subunits [NRPD1(NRPD1a) and NRPE1(NRPD1b)], have been implicated in the production and activity of 24-nt small RNAs (sRNAs) in RNA-directed DNA methylation (RdDM). Prevailing models support the view that PolIV(PolIVa) plays an upstream role in RdDM by producing the 24-nt sRNAs, whereas PolV(PolIVb) would act downstream at a structural rather than an enzymatic level to reinforce sRNA production by PolIV(PolIVa) and mediate DNA methylation. However, the composition and mechanism of action of PolIV(PolIVa)/PolV(PolIVb) remain unclear. In this work, we have identified a plant-specific PolV(PolIVb) subunit, NRPE5a, homologous to NRPB5a, a common subunit shared by PolI-III and shown here to be present in PolIV(PolIVa). Our results confirm the combinatorial diversity of PolIV(PolIVa)/PolV(PolIVb) subunit composition and indicate that these plant-specific Pols are eukaryotic-type polymerases. Moreover, we show that nrpe5a-1 mutation differentially impacts sRNAs accumulation at various PolIV(PolIVa)/PolV(PolIVb)-dependent loci, indicating a target-specific requirement for NRPE5a in the process of PolV(PolIVb)-dependent gene silencing. We then describe that the triad aspartate motif present in the catalytic center of PolV(PolIVb) is required for recapitulation of all activities associated with this Pol complex in RdDM, suggesting that RNA polymerization is important for PolV(PolIVb) to perform its regulatory functions.

Enhanced degradation of iprodione in soil after repeated treatments for controlling Sclerotinia minor

Poor field control of lettuce collar rot by iprodione was observed in southern France and was attributed to enhanced biodegradation of the fungicide. Enhanced biodegradation was obtained in vitro after repeated applications of iprodione to non-degrading soils. Normal soils became biodegrading after mixing with degrading soils (3 vol./1 vol.). Activity of the responsible microflora seemed dependent on soil physico-chemical characteristics.

Isolation from soil and growth characteristics of a cipc-degrading strain of Pseudomonas cepacia

Abstract A bacterial strain, identified as Pseudomonas cepacia , was isolated from soil and had the ability to utilize phenyl carbamates (BIPC, CIPC) as the sole source of carbon and energy. The degradation of CIPC, at various concentrations, was studied in a minimal medium. The addition of yeast extract increased bacterial growth, decreased the degradation-lag period, and increased the rate of CIPC transformation. The bacterial isolate also utilized 3-chloroaniline, the degradation product of CIPC. Its ability to degrade the herbicide was retained despite repeated growth in media without the herbicide.

Degradation of phenyl carbamate herbicides by Pseudomonas alcaligenes isolated from soil

Abstract A bacterial strain isolated from soil and identified as Pseudomonas alcaligenes, was able to hydrolyze four phenylcarbamate herbicides (CIPC, BIPC, IPC and swep) to corresponding anilines and alcohols by co-metabolism. The pH of the growth medium had little influence on bacterial growth and rate of herbicide transformation. Increase in CIPC and BIPC concentrations resulted in a significant inhibition of bacterial growth and herbicide degradation. Using a range of antibiotics it was shown that the enzyme involved in degradation was inducible.