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How plants maintain stable chlorophyll levels

Research team discovers new regulators coordinating chlorophyll synthesis and breakdown. Study published in Nature Communications

Darstellung von abgelösten Blättern
AFigure legend: Representative images of detached leaves
from wild-type, bcm1 bcm2 double mutant, BCM1
overexpression, and BCM2 overexpression seedlings
(from left side to right side) after 0 or 7 days of dark
incubation (DDI). Scale bars = 0.5 cm.

Chlorophyll is the most abundant pigment on earth, which enables vascular plants to absorb solar light energy to initiate photosynthesis. Seasonal color changes in leaves reflect dynamic accumulation of chlorophylls in response to various developmental and environmental cues. Dynamic control of chlorophyll levels is determined by the relative rates of chlorophyll biosynthesis and breakdown. It is widely accepted that chlorophyll biosynthesis is highly active during young leaf development, whereas chlorophyll is substantially degraded when plants enter the senescence phase. However, the molecular mechanisms behind the fundamental phenomenon and the potential post-translational regulatory link between chlorophyll synthesis and breakdown have not been revealed so far.

To address these longstanding questions, the researchers Dr. Peng Wang and Prof. Dr. Bernhard Grimm from the Plant Physiology group at the Humboldt University performed a reverse genetic screen for genes that might function in both chlorophyll synthesis and catabolism, and identified two paralogous genes in Arabidopsis, which were named BALANCE of CHLOROPHYLL METABOLISM (BCM) 1 and 2. Based on their data it is evident that BCM1 and BCM2 play conserved roles in both chlorophyll metabolic pathways to contemporaneously stimulate chlorophyll biosynthesis and suppress chlorophyll breakdown. Their functions in two antagonistic chlorophyll metabolic pathways apparently depend on the proteins with which they interact. The interaction of BCM1 with the Mg-chelatase-regulatory factor GENOMES UNCOUPLED 4 stimulates Mg chelation at the thylakoid membrane, whereas the interaction of each BCM isoform with the first enzyme of chlorophyll degradation, the dominant Mg-dechelatase isoform STAY-GREEN 1 reduces the stability of the enzyme.


Figure legend: Plants regulate chlorophyll levels to
optimize photosynthesis. Here Wang et al. describe
wo paralogous thylakoid proteins, BCM1 and BCM2,
that simultaneously stimulate chlorophyll biosynthesis
and attenuate chlorophyll degradation, thereby
conferring chlorophyll homeostasis during leaf growth.

Despite the similar functions of the two BCMs in chlorophyll metabolism, their expression patterns differ tremendously in the course of leaf development and senescence. While BCM1 is the predominant isoform during seedling growth, BCM2 is expressed during leaf senescence to control the chlorophyll content in older plants. Thus, this study supports a novel model in which the fine-tuning of dynamically changing chlorophyll levels from leaf emergence to senescence involves post-translational coordination of chlorophyll synthesis and breakdown, mediated by these evolutionarily conserved auxiliary factors BCM1 and BCM2.

Publication

Peng Wang, Andreas S. Richter, Julius R. W. Kleeberg, Stefan Geimer, Bernhard Grimm. “Post-translational coordination of chlorophyll biosynthesis and breakdown by BCMs maintains chlorophyll homeostasis during leaf development”.

Doi: doi.org/10.1038/s41467-020-14992-9 
Nature Communications, 11, 1254 (2020)

Link to the Study

Patent

Means and methods for conferring stay-green phenotype and controlling senescence in plants

Inventors: Dr. Peng Wang and Prof. Dr. Bernhard Grimm
Amtliches Aktenzeichen 20 163 425.0

Contacts

Dr. Peng Wang, Humboldt-Universität zu Berlin
Institut für Biologie/Pflanzenphysiologie

Phone: +49 030 2093-98339
wangpeng@hu-berlin.de

Prof. Dr. Bernhard Grimm, Humboldt-Universität zu Berlin
Institut für Biologie/Pflanzenphysiologie

Tel.: +49 030 2093-98330
bernhard.grimm@rz.hu-berlin.de

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