In contrast to animals, little is known about pattern formation in plants. Physiological and genetic data suggest the involvement of the phytohormone auxin in this process. Here, we characterize a novel member of the PIN family of putative auxin efflux carriers, Arabidopsis PIN4, that is localized in developing and mature root meristems. Atpin4 mutants are defective in establishment and maintenance of endogenous auxin gradients, fail to canalize externally applied auxin, and display various patterning defects in both embryonic and seedling roots. We propose a role for AtPIN4 in generating a sink for auxin below the quiescent center of the root meristem that is essential for auxin distribution and patterning.

We have developed a new community resource, called the WiscDsLox collection, for performing reverse-genetic analysis in arabidopsis. This resource is composed of 10,459 T-DNA lines generated using the Arabidopsis thaliana ecotype Columbia. The flanking sequence tag for each T-DNA insertion has been deposited in public databases, and seed for each line is currently available from the Arabidopsis Biological Resource Center. The pDsLox vector used to create this new population contains a Ds transposon and Cre/Lox recombination sites. Each WiscDsLox line therefore has the potential to serve as a launch-pad for performing local saturation mutagenesis by mobilization of the Ds element. In addition, Cre-Lox recombination between the T-DNA and a transposed Ds element should enable targeted deletion of specific genomic regions. We generated the WiscDsLox collection using an improved high-throughput pipeline that streamlines analysis of large numbers of independent Arabidopsis thaliana (L.) Hyenh. lines. In this paper we describe the details of this novel method and also provide potential users of WiscDsLox T-DNA lines with useful background information about this collection. Experiments to characterize the utility of the Ds transposon and Cre/Lox elements present in the WiscDsLox lines are in progress and will be reported in the future.

Using laboratory experiments, simulation models, and analytical techniques, we examined the impact of dispersal on the mean densities of patchily distributed populations. Even when dispersal leads to no net additions or removals of individuals from a population, it may nonetheless increase mean population densities if the net immigration rate is positive when populations are growing and negative when they are declining. As a model system for exploring this phenomenon, we used the yeastlike fungus Aureobasidium pullulans. In a laboratory experiment, we showed that dispersal can both ensure persistence and increase mean population densities even when dispersal among populations causes no direct addition or loss of fungal cells. From the laboratory data, we constructed a plausible model of A. pullulans dynamics among apple leaves within an orchard. This simulation model demonstrated that the effect of dispersal on mean densities is enhanced by three factors: weak density dependence of the dynamics within populations, high environmental variability affecting population growth rates, and lack of synchrony among the fluctuations of populations. Using an analytical model, we showed that the underlying mechanisms for this phenomenon are general, suggesting that a large effect of dispersal on mean population densities is possible in many natural systems.

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