Acreage Living, December 2004-January 2005

Newsletter for those who reside on acreages

Association with coregulators is the major determinant governing peroxisome proliferator-activated receptor mobility in living cells.

The nucleus is an extremely dynamic compartment, and protein mobility represents a key factor in transcriptional regulation. We showed in a previous study that the diffusion of peroxisome proliferator-activated receptors (PPARs), a family of nuclear receptors regulating major cellular and metabolic functions, is modulated by ligand binding. In this study, we combine fluorescence correlation spectroscopy, dual color fluorescence cross-correlation microscopy, and fluorescence resonance energy transfer to dissect the molecular mechanisms controlling PPAR mobility and transcriptional activity in living cells. First, we bring new evidence that in vivo a high percentage of PPARs and retinoid X receptors is associated even in the absence of ligand. Second, we demonstrate that coregulator recruitment (and not DNA binding) plays a crucial role in receptor mobility, suggesting that transcriptional complexes are formed prior to promoter binding. In addition, association with coactivators in the absence of a ligand in living cells, both through the N-terminal AB domain and the AF-2 function of the ligand binding domain, provides a molecular basis to explain PPAR constitutive activity.

Direct and indirect root defences of milkweed (Asclepias syriaca): trophic cascades, trade-offs and novel methods for studying subterranean herbivory

P>1. Entomopathogenic nematodes can function as indirect defence for plants that are attacked by root herbivores. By releasing volatile organic compounds (VOCs), plants signal the presence of host insects and thereby attract nematodes.2. Nonetheless, how roots deploy indirect defences, how indirect defences relate to direct defences, and the ecological consequences of root defence allocation for herbivores and plant biomass are essentially unknown.3. We investigate a natural below-ground tritrophic system, involving common milkweed, a specialist root-boring beetle and entomopathogenic nematodes, and asked whether there is a negative genetic correlation between direct defences (root cardenolides) and indirect defences (emission of volatiles in the roots and nematode attraction), and between constitutive and inducible defences.4. Volatiles of roots were analysed using two distinct sampling methods. First, we collected emissions from living Asclepias syriaca roots by dynamic headspace sampling. This method showed that attacked A. syriaca plants emit five times higher levels of volatiles than control plants. Secondly, we used a solid phase micro-extraction (SPME) method to sample the full pool of volatiles in roots for genetic correlations of volatile biosynthesis.5. Field experiments showed that entomopathogenic nematodes prevent the loss of biomass to root herbivory. Additionally, suppression of root herbivores was mediated directly by cardenolides and indirectly by the attraction of nematodes. Genetic families of plants with high cardenolides benefited less from nematodes compared to low-cardenolide families, suggesting that direct and indirect defences may be redundant. Although constitutive and induced root defences traded off within each strategy (for both direct and indirect defence, cardenolides and VOCs, respectively), we found no trade-off between the two strategies.6. Synthesis. Constitutive expression and inducibility of defences may trade off because of resource limitation or because they are redundant. Direct and indirect defences do not trade off, likely because they may not share a limiting resource and because independently they may promote defence across the patchiness of herbivore attack and nematode presence in the field. Indeed, some redundancy in strategies may be necessary to increase effective defence, but for each strategy, an economy of deployment reduces overall costs.

Acreage Living, December 1999, Vol 5, no.9

Acreage Living newsletter for those persons living on or interested in acreage living.

Acreage Living, March 2000, Vol 6, no.3

Acreage Living newsletter for those persons living on or interested in acreage living.

Acreage Living, May 2000, Vol.6, no.5

Monthly newsletter for people in Iowa that live on Acreages, produced by Iowa State University Copperative Extension.

Acreage Living, January 2000, Vol.6, no.1

Monthly newsletter for people in Iowa that live on Acreages, produced by Iowa State University Copperative Extension.

Acreage Living, February 2000, Vol.6, no.2

Monthly newsletter for people in Iowa that live on Acreages, produced by Iowa State University Copperative Extension.

Acreage Living, April 2000, Vol.6, no.4

Monthly newsletter for people in Iowa that live on Acreages, produced by Iowa State University Copperative Extension.

Acreage Living, June 2000, Vol.6, no.6

Monthly newsletter for people in Iowa that live on Acreages, produced by Iowa State University Copperative Extension.

Acreage Living, April 2002, Vol.8, no.4

Monthly newsletter for people in Iowa that live on Acreages, produced by Iowa State University Copperative Extension.

Acreage Living, July 2000, Vol.6, no.5

Monthly newsletter for people in Iowa that live on Acreages, produced by Iowa State University Copperative Extension.

Acreage Living, August 2000, Vol.6, no.8

Monthly newsletter for people in Iowa that live on Acreages, produced by Iowa State University Copperative Extension.

Acreage Living, September 2000, Vol.6, no.9

Monthly newsletter for people in Iowa that live on Acreages, produced by Iowa State University Copperative Extension.