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Jeffrey A. Long

 

Jeffrey A. Long

Jeffrey A. Long

Assistant Professor
Plant Molecular and Cellular Biology Laboratory

"A plant's shoot system is responsible for all of the above-ground portions of the plant, such as leaves, branches, and flowers, and is the site of photosynthesis. The root system lies below the ground and provides water and nutrients to the plant. My lab's research is focused on how a plant embryo sets up this apical/basal polarity."

Controlled by a tightly regulated choreography that determines what should go up and what should go down, plants develop along a polar axis with a root on one end and a shoot on the other. But scientists and home gardeners alike have been messing with plants' basic architecture for years. Permanently switch on a gene called BODENLOS (or "bottomless"), and they forgo root development altogether. Dip plant cuttings into hormone rooting powder, and roots start to sprout where none have been. The active ingredient, a synthetic version of the plant hormone auxin, which regulates root growth, overrides the molecular switch that keeps auxin-responsive genes turned off in parts of the plant that are above ground.

Long discovered that the switch is none other than a protein called TOPLESS. It had become clear that TOPLESS functions as a so-called co-repressor, which regulates gene expression by inhibiting the activity of transcription factors. Transcription factors control gene activity by binding to DNA sequences adjacent to a gene. But exactly how TOPLESS silences genes necessary for root development has remained unclear.

Hoping to gain insight into how TOPLESS functions by looking at the company it keeps, Long and his team searched for interacting partners in the plant Arabidopsis thaliana. This wee weed was the first flowering plant to have its genome unlocked and is loved by plant biologists for its short generation time. They discovered that BODENLOS, a transcriptional repressor that silences auxin-responsive genes, recruits the co-repressor TOPLESS to help with the job. While auxins are found throughout the whole plant, BODENLOS is only active in the shoot, ensuring that no accidental roots sprout above ground unless a gardener, "Dip'N Grow®" in hand, tips the balance.

Understanding how seedlings ensure that they are neither all shoot nor all root is fundamental to engineering plants that develop in ways that better suit agricultural needs.

Lab Photo

Left to right:
Naden Krogan, Andrew Ashbacher, Jeremy Gabriel, Rhiannon Biddick, Jeff Long, Peter T. Smith, Michael Hannon

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Jeffrey A. Long

Faculty

Jeffrey A. Long

Jeffrey A. Long

Assistant Professor
Plant Molecular and Cellular Biology Laboratory

Plants develop along a polar axis, with an apical shoot system at the top and a basal root system at the bottom. The shoot system is responsible for all of the above ground portions of the plant such as leaves, branches and flowers, and is the site of photosynthesis. The root system lies below the ground and provides water and nutrients to the plant. This shoot/root system develops early during plant embryogenesis and is fully formed in the mature seed.

My lab's research is focused on how this root/shoot system forms. In other words, we are interested in how a plant embryo develops apical/basal polarity. We are taking a genetic approach to answer this question using the plant model organism Arabidopsis thaliana. By isolating mutants that are disrupted in this process and then cloning the genes responsible, we are gaining insight into the molecular mechanisms the plant uses to determine its polarity. One mutant we have isolated, topless, transforms the apical shoot system into a second, basal root system, giving rise to a seedling with roots at both poles. We have cloned the gene responsible for this transformation and find it encodes a protein that prevents the transcription of root specific genes in the shoot system. We are currently cloning other genes that are involved in the same process, and have found that two of them are highly conserved with genes found in animals and humans.

  Figure 1. In a wild-type embryo, the root cap specific marker J1092 is expressed only in the root pole (1°). In topless-1 mutants, expression is found at both poles indicating a transformation from shoot to root fate (2°)

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