AsianScientist (Mar. 20, 2018) – Researchers at Tohoku University, Japan, have found that plants activate autophagy in their leaf cells to derive amino acids that are used for survival under energy-starved ‘hunger’ conditions. Their findings are published in Plant and Cell Physiology.
Plants use sunlight 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 sunlight 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 sunlight.
In the present study, a research group led by Dr. Masanori Izumi and Dr. Hiroyuki Ishida from Tohoku University in Japan showed that plants tide over ‘hunger’ using autophagy. Autophagy is the process by which intracellular proteins are broken down, and their constituent amino acids are recycled to sustain various cell functions. The researchers 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.
The researchers found that 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 is rapidly activated and amino acid levels increase. Moreover, plants lacking the machinery for autophagy are unable to effectively mount this response during the early stage of hunger stress.
The group also found that the levels of branched chain amino acids (BCAAs: valine, leucine, isoleucine) were elevated in wild-type Arabidopsis. Conversely, the increase in BCAAs are strongly compromised in mutant plants lacking the autophagy machinery.
“The mutants lacking enzymes required for the reuse of BCAAs as an energy source also showed reduced tolerance to hunger stress. We demonstrate that pathways to reuse BCAAs are coordinated with autophagy to overcome hunger stress in plants,” explained Izumi.
The researchers believe that a deeper understanding of mechanisms regulating chloroplast autophagy could provide new avenues to improve the productivity of cereal cultivation.
The article can be found at: Hirota et al. (2018) Vacuolar Protein Degradation via Autophagy Provides Substrates to Amino Acid Catabolic Pathways as an Adaptive Response to Sugar Starvation in Arabidopsis thaliana.
Source: Tohoku University; Photo: Shutterstock.
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