Genome-wide screening of budding yeast with honokiol to associate mitochondrial function with lipid metabolism.

Honokiol (HNK), an important medicinal component of Magnolia officinalis, is reported to possess pharmacological activities against a variety of diseases. However, the molecular mechanisms of HNK medicinal functions are not fully clear. To systematically study the mechanisms of HNK action, we screened a yeast mutant library based on the conserved nature of its genes among eukaryotes. We identified genes associated with increased resistance or sensitivity to HNK after mutation. After functional classification of these genes, we found that most HNK-resistant strains in the largest functional category were petites with mutations in mitochondrial genes, indicating that mitochondria were related to HNK resistance. Additional analysis showed that resistance of petite mutants to HNK was associated with upregulation of the ATP-binding cassette transporter Pdr5, which pumps out HNK. We also found that several HNK-sensitive mitochondria mutants were not petites, and had larger lipid droplets (LDs). Furthermore, HNK treatment on wild-type yeast cells seemed to disrupt mitochondrial morphology, induced triacylglycerol synthesis, and generated supersized LDs surrounded by mitochondria and endoplasmic reticulum (ER). These changes are also applied to atp7 mutant if no carbon resource was available. These results suggested that HNK treatment partly impaired normal mitochondrial function to form larger LDs by altering lipid metabolism.