The Maxwell lab takes a multidisciplinary approach towards understanding the role of the mitochondrion in a time-nested set of cellular responses from stress-sensing to acclimation and adaptation.  This research uses the model unicellular eukaryote Chlamydomonas and focuses primarily on function and regulation of the mitochondrial enzyme alternative oxidase (AOX) which is encoded by a family of nuclear genes (e.g. AOX1).  Research on Chlamydomonas is is aided by a wealth of molecular tools and genomic information and is of fundamental interest as it sheds light on the last common ancestor of animals and plants. 

Retrograde signal transduction

Many factors that induce AOX1 act by directly altering mitochondrial function. However, to-date little is known, for any eukaryote, about the intracellular components required for retrograde signalling from the mitochondrion to the nucleus. Defects in retrograde signalling are linked to aging and programmed cell death.  We are addressing this fundamental question using molecular genetic approaches based around insertional mutagenesis. We employ insertional mutagenesis in the isolation of mutants with altered AOX1 expression (Li et al. 2009) to identify intracellular components required for retrograde regulation. Current projects in the lab are involved in elucidating pathways of intracellular signalling involved in both the reactive oxygen and nitrate-dependent pathways that induced AOX1 expression.

Role of alternative oxidase in nitrate assimilation

In Chlamydomonas, AOX1 belongs in one of two gene clusters that are coordinately regulated by the nitrogen status of the cell. These so-called nitrate assimilation regulated, or NAR genes, are strongly induce by the nitrogen source nitrate. While AOX1 and AOX are strongly induced by nitrate, it remains largely unknown what role AOX serves in nitrogen assimilation. 

AOX Knockouts:  To address the function of AOX in metabolism we will be generating strains of C. reinhardtii in which AOX1 expression is silenced.  This will be accomplished using a recently described RNA interference (RNAi) technique.  The generation of RNAi strains will enable us to directly address two questions: (i) What role does AOX serve in nitrate assimilation in C. reinhardtii (Pakkiriswami et al., 2009) and (ii) are strains in which AOX is silenced more susceptible to oxidative stress. 

Extreme biology

Our laboratory is initiating a program of study on the Antarctic alga Chlamydomonas raudensis strain UWO241. This organism  was isolated from a lake in the Antarctic and is of interest to us because it is a psychrophile. That is, it is unable to grow above 20 C. The underlying biochemical basis for this phenotype is unknown. Our research on extreme biology is novel in that by having both psychrophilic and mesophilic strains of the same species (C. raudensis) we possess an unparalleled experimental system in which to explore biochemical adaptation to cold environments towards understanding the underlying basis of psychrophily.