Regulation of Cu delivery to chloroplast proteins

• Published in: Plant signaling & behavior Vol. 10; no. 7; p. e1046666
• Main Authors: Tapken, Wiebke, Ravet, Karl, Shahbaz, Muhammad, Pilon, Marinus
• Format: Journal Article
• Language: English
• Published: United States Taylor & Francis 03.07.2015
• Subjects: Addendum; Adenosine Triphosphatases - metabolism; Arabidopsis - metabolism; Arabidopsis Proteins - metabolism; Biological Transport; chloroplast; Chloroplast Proteins - metabolism; Clp protease; copper; Copper - metabolism; Evolution, Molecular; Homeostasis; Models, Biological; Molecular Chaperones - metabolism; P-type ATPase; PAA2/HMA8; plastocyanin; SPL7; CSD, Cu/Zn superoxide dismutase dismutase; Clp protease; SPL7, SQUAMOSA promoter binding protein-like7; Cu, copper; PPO, Polyphenol Oxidase; PAA2/HMA8; COPT, copper transporter; CSD, Cu/Zn superoxide dismutase; PCH1, Plastid Copper Chaperone 1; SPL7; PC, plastocyanin; homeostasis; Clp, caseinolytic protease; chloroplast; copper; plastocyanin; P-type ATPase; PAA1/2, P-type ATPase of Arabidopsis 1/2; CCS, copper chaperone for superoxide dismutase
• ISSN: 1559-2316; 1559-2324; 1559-2324
• DOI: 10.1080/15592324.2015.1046666

Plastocyanin is a copper (Cu)-requiring protein that functions in photosynthetic electron transport in the thylakoid lumen of plants. To allow plastocyanin maturation, Cu must first be transported into the chloroplast stroma by means of the PAA1/HMA6 transporter and then into the thylakoid lumen by the PAA2/HMA8 transporter. Recent evidence indicated that the chloroplast regulates Cu transport into the thylakoids via Clp protease-mediated turnover of PAA2/HMA8. Here we present further genetic evidence that this regulatory mechanism for the adjustment of intra-cellular Cu distribution depends on stromal Cu levels. A key transcription factor mediating Cu homeostasis in plants is SQUAMOSA promoter binding protein-like7 (SPL7). SPL7 transcriptionally regulates Cu homeostasis when the nutrient becomes limiting by up-regulating expression of Cu importers at the cell membrane, and down-regulating expression of seemingly non-essential cuproproteins. It was proposed that this latter mechanism favors Cu delivery to the chloroplast. We propose a 2-tiered system which functions to control plant leaf Cu homeostasis: SPL7 dependent transcriptional regulation of cuproproteins, and PAA2/HMA8 turnover by the Clp system, which is independent on SPL7.