All organisms must perceive, process and react to environmental signals in order to survive and pass their genetic material onto the next generation. One of the most important signaling pathways for plant systems is that which begins with the perception of sunlight. This process, known as de-etiolation or “greening”, is mediated by the phytochrome (phy) family of photoreceptors. Upon absorption of red light, these photoreceptors translocate from the cytosol to the nucleus, where they bind to and trigger the degradation of a set of transcription factors known as PHYTOCHROME-INTERACTING FACTORS (PIFs). The degradation of the PIFs results in a cascade of transcriptional changes that enable a seedling to turn from yellow to green in less than 24 hours. At the center of this developmental reprogramming lie the mitochondria and plastids, which must rapidly respond to light signals so that they can mobilize the energetic resources necessary for synthesizing the proteins and pigments that drive photosynthesis.
Approximately 25% of the PIF-induced genes whose transcript levels change after only one hour of illumination encode a class of proteins called micropeptides (Calderon et al., 2022, Plant Physiol). Micropeptides are small (less than 150 amino acids) and often cell-to-cell mobile. They have many important roles in mammalian systems, including in regulating mitochondrial metabolism. Plastids, like mitochondria, are organelles that are descended from once free-living bacteria. Given their similar endosymbiotic origins, we hypothesize that plant mitochondria and plastids may also depend on micropeptides for the proper regulation of their development and activity.
Using genetics, biochemistry, microscopy and molecular biology, we are investigating the function of these micropeptides and have found that they appear to play an important role in coordinating metabolism between mitochondria and chloroplasts during the switch from heterotrophy to photoautotrophy. We are continuing to explore the role of micropeptides throughout the green lineage (cyanobacteria, algae & plants) with the intention of discovering the ways in which they regulate photosynthesis and respiration, as well as plant development. We expect that the rewiring of micropeptide-mediated regulation of plant metabolism through genetic engineering will be a potential pathway for increasing crop yield and food security.
Transient expression of a fluorescently-tagged light-regulated micropeptide in Nicotiana benthamiana showing mitochondrial localization. Nucleus is labeled in blue (DAPI), chloroplasts in red (chlorophyll) and the micropeptide in yellow (mCitrine).