memory molecules in plants

Indian biologist discovers memory molecules in plants G.S. Mudur New Delhi, April 26: An Indian biologist has discovered in plants special proteins, called prions, hitherto found in yeast, insects, and mammals that could explain the decades-old mystery of how even plants form memories. Sohini Chakrabortee, who spent three years scanning over 20,000 proteins in plants from the mustard family, has found at least one protein that behaves like a prion and is capable of building molecular memories, such as those of exposure to a prolonged period of cold that precedes flowering. Prions are a unique class of proteins that can alter their shapes, self-propagate by inducing other molecules of same protein to adopt their shapes, and cluster together. While prions were detected in the early-1980s playing a role in the transmission of certain neurodegenerative brain disorders, studies in fruit-flies and mice over the past five years have suggested that prion-like proteins may be essential in maintaining long-term memories in these organisms. "This is the first evidence that a plant protein may self-replicate as a prion - this opens up the possibility of protein-based memories in plants," said Chakrabortee, who led the research as a post-doctoral fellow in the laboratory of Susan Lindquist at the Whitehead Institute for Biomedical Research at the Massachusetts Institute of Technology in the US. Several studies over the past three decades have suggested plants also form memories of exposure to drought, heat, or prolonged cold. "It is these memories that allow plants to distinguish between a single night of cold and a long winter," said Chakrabortee, who had studied plant biology at Delhi University before pursuing a PhD at the University of Cambridge in the UK. In their study, Chakrabortee and her colleagues searched a plant protein database and identified three proteins with prion-like properties involved in flowering - and found that at least one of these appears capable of forming molecular memories. "When we talk about plant memories, we mean the plant that has a memory responds differently to a stimulus compared to a plant that has never experienced this before," said Can Kayatekin, a post-doctoral associate and a member of the Whitehead-MIT team. The study's findings described on Monday in the US journal Proceedings of the National Academy of Sciences, have excited biologists who have long been familiar with prions as primarily linked to neurodegenerative brain diseases in animals and humans. "This is really, really significant, I have never, never heard of prions in plants - and I've been studying prions for about twenty years," Karim Adjou, professor at the Veterinary School of Alfort in France told The Telegraph in a telephone interview. "If this is confirmed, it will open up a completely new area of research." Prion research emerged in the 1980s amid discoveries that these self-propagating proteins can explain Mad Cow disease, spread through contaminated beef, and Kuru, another brain disorder linked to the practice decades ago of funerary cannibalism in a tribe in Papua New Guinea. Since then, prions have also been implicated in some other neurodegenerative disorders. But over the past decade, studies by the Nobel laureate neuroscientist Eric Kandel at Columbia University and India-born, Calcutta-educated neurobiologist Kausik Si at the Stowers Institute of Medical Research in the US have indicated that prion-like proteins can help build long-term memories. Neuroscientists believe long-term memories are stored in the brain through connections between neurons, or brain cells. But these physical connections need to be maintained for days, months, or years, for specific memories to persist. Kandel and Li are among scientists whose work suggests that prion-like proteins may be among molecules that can explain the persistence of memories. Prions tend to stick together and form sticky aggregates, or clusters. As long as these aggregates persist, long-term memories persist, Kandel had said last year in a media statement released by Columbia University describing his research. "Prion aggregates renew themselves continually recruiting new prions into the aggregates - this maintenance is crucial for memories." "The finding of prions in plants could explain some unresolved puzzles of flowering," said Ranabir Das, a senior scientist at the National Centre for Biological Sciences, Bangalore, who has himself studied prions but was not associated with the Whitehead-MIT research. "While the flowering process is generally understood, plants appear to somehow fine-tune their behaviour to external cues - and prion-driven mechanisms may help explain that," Das said. Jayant Udgaonkar, another senior scientist at the NCBS, said the identification of proteins with prion-like behavior in plants is an important development as it supports earlier work on other organisms showing that prion-like proteins have important physiological roles. "The prion-like structure is part of a protein involved in flowering," Udgaonkar said. "It is a likely candidate for a protein-enabled memory mechanism in plants that would enable plants to use the memory of external weather in the regulation of its physiology." Chakrabortee, who has moved to the University of Birmingham to take on the role of a research administrator, says the most exciting aspect of the study is the finding of prion-like proteins in the plant kingdom.