The Arabidopsis AtcDPPIV gene encodes a chloroplast-localized protein that has homology to animal proteases that cleave off the first two amino acids from the amino terminus of substrates that have a proline as the second amino acid. AtcDPPIV mRNA is abundant when plants are grown in low light, but is greatly reduced after two days at sub-saturating moderate light. The decrease in AtcDPPIV mRNA levels is not observed when the cch1 mutant is transferred from low to moderate light. The cch1 mutant has a smaller light harvesting complex under moderate light, and is therefore harvesting less light than WT under moderate light. These observations suggest that AtcDPPIV gene expression correlates with light harvesting, not just light intensity. To understand the function of AtcDPPIV, two mutants with independent T-DNA insertions into the AtcDPPIV gene have been analyzed. These lines show subtle photoacclimation phenotypes suggesting that the AtcDPPIV dipeptidyl aminopeptidase may play a role in adjusting plants to different light intensities. To test this hypothesis, six objectives are proposed: 1) Demonstrate that the photoacclimation phenotypes in the two insertion lines are due to loss of AtcDPPIV by complementation with AtcDPPIV. 2) Overexpress AtcDPPIV and AtcDPPIV::GFP to determine if overexpression results in a photoacclimation phenotype. 3) Overexpress AtcDPPIV::GFP to confirm predicted chloroplast localization and produce an AtcDPPIV antibody for suborganelle localization. 4) Determine the substrate specificity of recombinant AtcDPPIV protease. 5) Use the yeast two-hybrid system to identify proteins that interact with AtcDPPIV. 6) Characterize the extended and compact growth habits observed during photoacclimation in more detail, and determine whether subtle effects are occurring in the AtcDPPIV insertion lines.
Little is known about signaling during photoacclimation, and the AtcDPPIV dipeptidyl aminopeptidase could be part of an important signaling cascade that has not yet been described. The AtcDPPIV protein is highly conserved in dicots, monocots and in numerous environmental bacteria, suggesting that it has an important, conserved function.
Broader Impacts The broader impacts of this proposal include the training of undergraduate and Masters students from a minority campus in Southern California. The best way to increase the numbers of underrepresented minorities in research careers is to offer them an interesting, challenging, feasible project at an early stage in their studies. Also included is the training of a postdoctoral researcher in effective teaching as well as excellence in research. Many of the projects in the laboratory have been included in the undergraduate curriculum in Biological Sciences in both lower and upper division courses, and thus a large number of students have been impacted by this work. In addition, the PI coordinates a third grade science teaching project that currently provides an eight-week hands-on science program to 160 third grade students in the Long Beach public school system.
