Universidad del Estado de Arizona. USA.
RESUMEN (ABSTRACT)
Integrating the in planta roles of the proton-pumping pyrophosphatase in the regulation and efficiency of carbon utilization and transport
Dr. Roberto Gaxiola
Profesor investigador del Departamento de Biociencias Celulares y Moleculares de la Universidad del Estado de Arizona, USA
Plant productivity is determined in large part by the partitioning of assimilates between the sites of production and the sites of utilization. To judiciously engineer increased yield of crop plants, a better understanding of the regulation and efficiency of in planta carbon utilization and transport is required. Evidence from our laboratory and others show that proton-pumping pyrophosphatases (H+-PPases) enhance many energetic plant processes including general growth (biomass accumulation), nutrient acquisition, CO2 fixation and stress responses. We hypothesize that H+-PPases have different and seemingly contradictory functions in planta depending on their organ and membrane localization. These functions range from the well-documented PPi (pyrophosphate) hydrolysis coupled with H+-pumping activity in vacuolar membranes to PPi synthesis at the expense of the proton motive force (pmf) of the plasma membrane (PM) in phloem cells. We further hypothesize that the versatility of the H+-PPase has a direct impact on plant PPi metabolism with implications for sucrose synthesis, partitioning and utilization. We are currently testing three independent, but not mutually exclusive, hypotheses that H+-PPases have the following distinct functions in different tissues: 1. The vacuolar H+-PPase participates in cytosolic PPi scavenging in mesophyll cells, and that its overexpression enhances this scavenging capacity to favor sucrose synthesis; 2. The H+-PPase that localizes to the PM of the sieve element/companion cell complex functions as a PPi synthase and utilizes the pmf to regulate and maintain the cytosolic PPi levels required for efficient sucrose respiration. This generates the ATP for the maintenance of the pmf required for phloem loading, and an increased activity enhances phloem loading and transport capacity; 3. In actively dividing cells of sink tissues, the H+-PPase acidifies the lumen of nascent vacuoles to conserve ATP and to scavenge cytosolic PPi to prevent its well-documented feedback inhibitory effect on biosynthetic pathways. The up-regulation of the H+-PPase enhances these functions and increases sink strength. We are testing these individual hypotheses via genetic, molecular, metabolomic, and immunohistochemical (ultra-structural) approaches.