Defining Whole-Plant Phloem Function with Molecular Studies of Anatomy

University Of Maryland, College Park, College Park MD

Investigators

Abstract

To link the long-distance fluid mechanical behavior of sugar transport in the phloem vasculature of plants with the short-distance regulation of sugar exchange between the phloem and surrounding tissue requires much deeper knowledge of the phloem's quantitative anatomy than is currently available. Accurate measurements of phloem anatomy are now possible with live-cell imaging of transgenic Arabidopsis plants that express mCitrine (monomeric yellow fluorescent protein, YFP)-labeled plasma membrane proteins in phloem sieve elements. Some of these transgenics (developed by the PI) provide excellent illumination of sieve elements for confocal laser scanning microscopy (even through live tissue). Sieve plates and pores show thorough YFP labeling, holding out the promise for immunohistochemical fluorescence imaging of fixed and sectioned tissues. The PI is currently exporting successful constructs to other species, including Nicotiana benthamiana, N. tabacum, and Populus, for cross-species comparisons of phloem anatomy. The results will help the PI to predict the gross-scale physicochemical behavior of the phloem across a set of species and plant organs, which will provide the context for other experiments, such as "black-box" manipulations of whole-plant source and sink strength using local and chemically inducible silencing of phloem-specific transporters. Analysis of the constructs will also aid in understanding how proteins expressed in nucleate companion cells are trafficked to enucleate sieve elements. The broader impacts of this study include a "re-invention" of American phloem biology to cut across disciplines, drawing from applied mathematics, systems biology, and molecular genetics, as well as a truly interdisciplinary opportunity for undergraduate training. The work could be very important for our understanding of the movement of phloem-borne plant diseases, plant resource allocation, and the role of trees in the global carbon cycle.