Chemical Approaches for Gibberellins Transport Exploration

Roy Weinstain, Molecular biology and ecology of plants, Tel-Aviv University, Tel-Aviv, Israel
Iris Tal, Molecular biology and ecology of plants, Tel-Aviv University, Tel-Aviv, Israel
Naama Rubinsein, Molecular biology and ecology of plants, Tel-Aviv University, Tel-Aviv, Israel
Eilon Shani, Molecular biology and ecology of plants, Tel-Aviv University, Tel-Aviv, Israel
Yi Zhang, Division of biological sciences, University of California San Diego, San Diego, United States
Mark Estelle, Division of biological sciences, University of California San Diego, San Diego, United States

Gibberellins (GA) are a tetracyclic diterpenoid class of plant hormones that direct key processes in plants development and adaptive growth. Consequently, plants tightly regulate their GA response pathways at multiple levels including biosynthesis, metabolism, perception, and signaling. Interestingly, plants exhibit the unique ability to regulate their hormones’ distribution, as illustrated most clearly in the case of polar auxin transport. Although studies with radiolabeled GA and mutant grafting established GA mobility throughout plants, little is known about either GA distribution patterns or the mechanisms shaping them. Chemical tools are particularly suitable to dissect such biological mechanisms as they enable probing and manipulation at the molecular level. Thus, we are developing specific chemical tools, such fluorescent- and caged-GA, and employing them in conjunction with molecular biology, genetic and imaging techniques to explore GA transport in plants.

Using fluorescently labeled bioactive GA, we show that GA form distinct distribution patterns in Arabidopsis Thaliana roots, accumulating specifically in elongating endodermal cells. Pharmacological studies, along with examination of mutants affected in endodermal specification indicate that this is an active and highly regulated process. To obtain better spatio-temporal control over the monitoring of native GA movement, we are developing caged-GA and combining them with RGA-GFP, serving as a GA-sensor. Successful coalescence of these techniques would enable identifying GA trafficking pathways and quantitative measurement of kinetics. To further understand the genetic regulation behind GA active transport, we initiated reverse genetic screens, using the specific distribution of the fluorescent-GA as readout. The screen, hitherto, revealed a protein from the NRT/PTR family that disrupts the specific accumulations of fluorescent-GA compared to wildtype plants. Miss-expression of the gene under a p35S constitutive promoter results in indiscriminate uptake of fluorescent-GA into all root cells. We are currently characterizing the potential roles of this first putative GA transporter.