DGIST reveals how “switch” in aging of plant leaves works

□ A joint research team led by Professors Pyungok Lim, Jongchan Lee, and Minsik Kim from Daegu Gyeongbuk Institute of Science & Technology (DGIST; President Kunwoo Lee) has discovered a new molecular switch that determines when plant leaves begin to age. The research team has identified for the first time a new mechanism in which RNA made from the nucleus moves to chloroplasts and regulates the aging of plant leaves.

□ While chloroplasts in plant leaves produce primary energy resources for plant growth through photosynthesis, they degrade and become resources themselves as they start to age. The degraded chloroplast resources move to the seeds, where they are used as nutrients for the next generation, or are sent to the stems or roots, where they are used to prepare for the next season. Although this “functional switch of chloroplasts” is directly related to the survival and reproductive strategies of plants, exactly how the timing of this switch is regulated has previously not been well understood.

□ The research team discovered a new regulatory factor called “chlorella RNA” through a genetic analysis of long non-coding RNAs (lincRNAs).^[1] It exhibits patterns of chloroplast gene expression similar to those in the model plant Arabidopsis thaliana. Using a multidisciplinary approach that combined high-resolution mass spectrometry and single-molecule imaging techniques, the research team suggested that chlorella RNA is transcribed in the nucleus, moves through the cytoplasm to chloroplasts, and binds to proteins of the plastid-encoded RNA polymerase complex (PEP complex) involved in the transcription of genes present in chloroplasts. It can subsequently affect the transcriptional regulation activity of chloroplasts and switch the function of chloroplasts depending on the level of expression.

□ The research team also confirmed that the GLK transcription factor^[2] regulates the expression of chlorella RNA. They identified that GLK maintains the photosynthetic function during the growth period by increasing the expression of chlorella RNA, but its activity decreases with the beginning of aging, resulting in a decline in chlorella RNA and the consequent loss of the photosynthetic function and degradation of chloroplasts.

□ “This study holds huge academic significance as it suggests how long non-coding regulatory RNAs are spatiotemporally regulated in aging, a subject matter that has not been researched well due to methodological limitations,” said Professor Pyungok Lim. “The findings of this study were obtained from a variety of interdisciplinary studies, such as bioimaging technology that showed RNA migration tracking and the identification of proteins that interact with RNAs.” “This approach could serve as a cornerstone for understanding a variety of biological phenomena based on long non-coding RNAs,” he added. He also said that it could “increase the photosynthetic efficiency and productivity of crops” by regulating the development and aging of plant leaves.

□ Dr. Myeonghoon Kang and Dr. Joohyun Lee, under the research team led by Professor Pyungok Lim (co-corresponding author) and Jinkwang Kim, a student under the research team led by Professor Jongchan Lee (co-corresponding author), took part in this study as the first authors, and the research teams of Professor Minsik Kim (co-corresponding author), Professor Junemyoung Kwak (co-author), and Professor Seongwook Yang at Yonsei University (co-author) participated. This study was funded by the National Research Foundation of Korea’s Mid-Career Researcher Support Program and Basic Laboratory Program, and its findings were published in Nature Plants (IF 13.6), one of the world’s top botany journals.

^[1] Long non-coding RNA (lncRNA): Long RNA molecule that does not make proteins but regulates gene expression in cells or delivers signals. In other words, it does not create the blueprint for proteins but acts as a “conductor” to regulate how other genes work.

^[2] Golden2-like transcription factor (GLK transcription factor): Protein that switches on and off genes related to photosynthesis in plant cells and regulates the development of chloroplasts during leaf growth.