Researchers at Tohoku University have found that plants activate autophagy in their leaf cells to derive amino acids that are used for survival under energy-starved "hunger" conditions. The findings show that amino acid utilization in plants can be controlled by the manipulation of autophagy.
Plants use solar energy for growth through a process known as photosynthesis. Photosynthesis reactions occur in chloroplasts, which are the intracellular compartments in green organs, mainly in leaves. In nature, plants cannot get enough solar energy when neighboring plants shade them from the sun. Under agricultural fields, insufficient sunshine due to unusual weather, or natural disasters such as flooding, strongly inhibits energy acquisition in crop plants. Therefore, many researchers are interested in how plants cope with their "hunger" due to the shortage of solar energy.
Drs. Masanori Izumi and Hiroyuki Ishida from Tohoku University had previously demonstrated that plant chloroplasts are actively digested via a process of autophagy during energy starvation. Autophagy is the "self-eating" process of consuming the portion of intracellular proteins in the cells of eukaryotes such as yeast, humans and plants. The research group focused on the precise role of chloroplast-targeted autophagy in the plant survival strategy under low-energy stress. "We hypothesized that chloroplast-associated autophagy is closely linked to the amino acid metabolism in energy-starved plants", said Izumi.
According to the study, when a cress plant known as Arabidopsis thaliana is exposed to hunger stress as plants are transferred into complete darkness they can continue to grow for several days; autophagic digestion of chloroplast proteins are rapidly activated and amino acid levels increase. This response during the early stage of hunger stress is suppressed in the mutant plants lacking autophagy machinery.
Plants after being placed in an energy-starved environment (darkness) for 4 days and then returned to a normal environment for a week. The wild-type Arabidopsis on the left survives and restarts normal growth well, but the double mutant of autophagy machinery and an amino acid metabolism on the right, which cannot activate autophagic digestion, dies.
The amino acid recycling is important in crop productivity, as amino acids derived from protein breakdown are mobilized and stored in seeds in cereal crops before harvest. The current findings show the possibility that the manipulation of autophagy allows plants to modify their amino acid use. The researchers believe that further elucidation of regulation mechanisms of chloroplast autophagy could provide new avenues to improve the quality or productivity in cereal cultivation.
- Publication Details:
Title: Vacuolar Protein Degradation via Autophagy Provides Substrates to Amino Acid Catabolic Pathways as an Adaptive Response to Sugar Starvation in Arabidopsis thaliana
Authors: Takaaki Hirota, Masanori Izumi, Shinya Wada, Amane Makino, Hiroyuki Ishida Journal: Plant & Cell Physiology
Name: Masanori Izumi
Frontier Research Institute for Interdisciplinary Sciences, Tohoku University