Jianping Hu

Core Faculty, Plant Focus, DOE - Project A Faculty, DOE - Project B Faculty

Professor

Department of Plant Biology
huji@msu.edu

Research: Molecular Mechanisms of Energy Organelle Dynamics and Interorganellar Interaction and Communication

In eukaryotic cells, biochemical reactions are compartmentalized in specific subcellular organelles. Plant mitochondria, peroxisomes, and chloroplasts are essential organelles in development and coordinate in a number of metabolic pathways required for energy capture, conversion, and metabolism. The Hu laboratory is interested in understanding molecular mechanisms underlying the dynamic behavior of peroxisomes and mitochondria and how peroxisome metabolism influences photosynthesis in the chloroplast at the mechanistic level.

For adaptation, subcellular organelles can alter their abundance, morphology, and protein composition depending on the developmental and environmental conditions. One research goal of the Hu lab is to elucidate molecular mechanisms by which peroxisomes and mitochondrial proliferate to ultimately understand how organelle dynamics contribute to changes in plant physiology and development. To this end, we have identified and characterized components of the machineries that govern the biogenesis, division and proliferation of peroxisomes and mitochondria (Fig. 1) and revealed transcriptional and post-translational regulatory mechanisms of these processes. Recent effort is on understanding the regulatory role of proteases and ubiquitin-proteasome mediated proteolysis in peroxisome and mitochondrial biogenesis and division and in plant stress response.

Perixosome and mitochondrial division — Figure 1. Peroxisome and Mitochondrial Division 1 (PMD1) is a component of the peroxisome and mitochondrial division/proliferation machinery. Confocal images were taken from leaf epidermal cells of *PMD1* loss-of-function mutant and overexpressor, showing abnormal morphologies of peroxisomes and mitochondria that are fluorescently labeled by organelle marker proteins CFP-PTS1 and COX4-YFP, respectively. Scale bar = 10 m.

The Hu lab also collaborates with other labs in the PRL and on campus to study the impact of peroxisomal metabolism on photosynthesis, a fundamental process that occurs in chloroplasts and is subject to regulation by cellular and external environmental cues. Peroxisomes are often found to be physically associated, and act collaboratively, with chloroplasts. Using the Dynamic Environment Phenotype Imager (DEPI), we have screened our collection of Arabidopsis peroxisome mutants and identified those mutants showing photosynthetic deficiencies under light conditions that are more relevant to the natural environment. Currently we focus on understanding the regulatory links between photorespiration and photosynthesis under dynamic environmental conditions (Fig. 2).

Photosynthetic phenotypes of peroxisome mutants — Figure 2. Photosynthetic phenotypes were revealed in peroxisomal mutants under dynamic light conditions. Shown are heatmaps of four photosynthetic parameters, ?2, NPQ, qE and qI, in mutant relative to the WT. In each heatmap, x axis is time points, y axis is the ~150 peroxisomal mutants subjected to the screen, and the five columns represent five days of dynamic light treatment. The subgroup of mutants with lower ?2 is indicated by the black box, and mutants in this subgroup are linked to each other between the heatmaps by curved lines. Color code is under each heatmap to indicate the level of changes.

Our research has agricultural and economical relevance, as knowledge gained may provide molecular bases for developing strategies for rational engineering of crop plants to improve metabolism, bioenergy production, and defense against environmental stresses. Our research may also provide useful information to biomedical studies in curing human peroxisomal and mitochondrial diseases.