Mechanisms driving root pressure in Z. mays—a transcriptomic approach

Authors: DROBNITCH, SARAH - Colorado State University; Wenz, Joshua; Gleason, Sean; Comas, Louise

Submitted to: Journal of Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/28/2024
Publication Date: 3/5/2024
Citation: Drobnitch, S.T., Wenz, J.A., Gleason, S.M., Comas, L.H. 2024. Mechanisms driving root pressure in Z. mays—a transcriptomic approach. Journal of Plant Physiology. 296. Article 154209. https://doi.org/10.1016/j.jplph.2024.154209.
DOI: https://doi.org/10.1016/j.jplph.2024.154209

Interpretive Summary: Root pressure, the positive flow of water and sap from the base of plants, occurs in many crop species during drought recovery. Despite observing root pressure for over 150 years and linking it to productivity following drought, scientists are still unable to identify the mechanism by which it is generated. In this study, we compared the genes being expressed in maize plants generating root pressure versus those that were not. Of this subset of differentially expressed genes, we searched for genes with a possible relevance to generating this pressure. We found many genes of interest, such as transporters and ion channels that move water across cell membranes. These differentially expressed genes were found in the stem and roots, but not in the fine roots. We concluded that either fine roots either do not help create the pressure, or they are always making pressure. Identifying these genes and tissues where they are expressed is critical for narrowing down the specific mechanisms generating root pressure and enable us to incorporate enhanced root pressure into future drought-tolerant crops.

Technical Abstract: While there are many theories and a variety of innovative datasets contributing to our understanding of the mechanism generating root pressure in vascular plants, we are still unable to produce a specific cellular mechanism for any species. To discover these mechanisms, we used RNA-Seq to explore differentially expressed genes in three different tissues between individual Zea mays plants expressing root pressure and those producing none. Working from the perspective that roots cells are utililizing a combination of an osmotic exudation and hydraulic pressure mechanisms to generate positively-pressured flow of water into the xylem from the soil, we hypothesized that differential expression analysis would yield candidate genes coding for membrane transporters and cotransporters, ion channels, ATPases, and hormones with clear relevance to root pressure generation. In basal stem and coarse root tissue, we observed these classes of differentially expressed genes and more, including a strong cytoskeletal remodeling response. Fine roots displayed remarkably little differential expression relevant to root pressure, leading us to conclude that they either do not contribute to root pressure generation or are constitutively expressing root pressure mechanisms regardless of soil water content.