Chlorophyll Degradation Mechanisms in Plant Senescence

Chlorophyll degradation is a highly regulated process that underpins nutrient remobilisation and the visible yellowing of leaves, fruits and petals during senescence. This process follows the conserved PAO–phyllobilin pathway, in which chlorophyll a is first converted to pheophytin a by removal of its central magnesium ion or via direct dephytylation. Pheophytin a is then hydrolysed to pheophorbide a by pheophytinase, and subsequently oxidised by pheophorbide a oxygenase to yield the red chlorophyll catabolite. A non-enzymatic isomerisation within the vacuole produces nonfluorescent chlorophyll catabolites, facilitating safe storage and preventing photo-oxidative damage. Key regulators such as the STAY-GREEN (SGR/NYE1) protein and chlorophyll b reductases (NYC1/NOL) coordinate the disassembly of light-harvesting complexes, ensuring dismantling of photosystem components. Phytohormones—particularly ethylene and abscisic acid—intersect with light signalling networks via transcription factors such as HY5 and EIN3/EIL1 to modulate expression of catabolic enzymes. Recent advances have revealed post-translational scaffold proteins, notably BALANCE OF CHLOROPHYLL METABOLISM (BCM) paralogs, that dynamically balance biosynthetic and catabolic fluxes to maintain chlorophyll homeostasis. While the core biochemical route is conserved, tissue-specific dephytylation mechanisms distinguish leaf senescence from fruit ripening and petal degreening, reflecting diverse ecological functions of chlorophyll breakdown in recycling, stress resilience and horticultural traits.

Research from Nature Portfolio

Research has uncovered how post-translational regulators fine-tune chlorophyll turnover at different developmental stages. Two BCM paralogs in Arabidopsis act as scaffold proteins: during early leaf expansion, BCM1 promotes magnesium chelation by stimulating Mg-chelatase and suppresses chlorophyll breakdown by targeting Mg-dechelatase for degradation. At the onset of senescence, BCM2 expression rises to attenuate catabolic activity, thereby preventing excessive chlorophyll loss. This study provides a molecular framework for how plants coordinate opposing biosynthetic and catabolic pathways via dynamic protein–protein interactions, ensuring optimal photosynthetic performance and orderly senescence.

Chlorophyll Degradation Mechanisms in Plant Senescence publication trend

The graph below shows the total number of articles in chlorophyll degradation mechanisms in plant senescence across all publications each year (not limited to Nature Index journals).

Technical terms

PAO–phyllobilin pathway: A sequential chlorophyll breakdown route involving pheophorbide a oxygenase and formation of phyllobilins.

Dephytylation: Removal of the phytol side chain from chlorophyll, typically by chlorophyllase or pheophytinase, initiating catabolism.

Pheophorbide a oxygenase (PAO): Enzyme that opens the chlorin macrocycle of pheophorbide a to form red chlorophyll catabolite.

STAY-GREEN (SGR/NYE1): Regulatory protein that facilitates chlorophyll breakdown by recruiting catabolic enzymes to light-harvesting complexes.

Chlorophyll b reductase (NYC1/NOL): Enzyme complex that converts chlorophyll b to 7-hydroxymethyl chlorophyll a, a key early step in turnover of light-harvesting complexes.

BALANCE OF CHLOROPHYLL METABOLISM (BCM): Post-translational scaffold proteins that coordinate opposing chlorophyll biosynthesis and catabolism during leaf development and senescence.

Phytohormones: Plant hormones such as ethylene and abscisic acid that modulate gene networks governing chlorophyll degradation in response to developmental and environmental cues.

References

1. Chlorophyllase (PsCLH1) and light-harvesting chlorophyll a/b binding protein 1 (PsLhcb1) and PsLhcb5 maintain petal greenness in Paeonia suffruticosa ‘Lv Mu Yin Yu’. Journal of Advanced Research (2024).
2. Transcription factors MdEIL1 and MdHY5 integrate ethylene and light signaling to promote chlorophyll degradation in mature apple peels. Horticulture Research (2024).
3. Phytohormone and Light Regulation of Chlorophyll Degradation. Frontiers in Plant Science (2017).
4. Identification of a Novel Chloroplast Protein AtNYE1 Regulating Chlorophyll Degradation during Leaf Senescence in Arabidopsis. Plant Physiology (2007).
5. Participation of Chlorophyll b Reductase in the Initial Step of the Degradation of Light-harvesting Chlorophyll a/b-Protein Complexes in Arabidopsis *. Journal of Biological Chemistry (2009).
6. Different Mechanisms Are Responsible for Chlorophyll Dephytylation during Fruit Ripening and Leaf Senescence in Tomato. Plant Physiology (2014).
7. Post-translational coordination of chlorophyll biosynthesis and breakdown by BCMs maintains chlorophyll homeostasis during leaf development. Nature Communications (2020).