CORNICHON HOMOLOG 5-dependent ER export of membrane cargoes in phosphate-starved Arabidopsis root as revealed by membrane proteomic analysis
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To find potential membrane cargoes of Arabidopsis thaliana CORNICHON HOMOLOG 5 ( At CNIH5), a phosphate (Pi) deficiency-induced ER cargo receptor, we applied the UV-cleavable 4-hexylphenylazosulfonate (Azo)-solubilized microsomal protein extraction for iTRAQ-based proteomic analysis and identified 106 downregulated proteins in the Pi-limited roots of cnih5 , including PHOSPHATE TRANSPORTER 1 proteins (PHT1s) and transmembrane enzymes responsible for the biosynthesis of very long-chain fatty acids and their derivative extracellular aliphatic compounds, and nucleotide sugar for cell walls.
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We confirmed the interaction of At CNIH5 with several downregulated transporters in cnih5 , including At PHT1s, At OCT1, At URGT6, At DTX21, and At DTX35, using the yeast split-ubiquitin and the in-planta tripartite split-GFP assays.
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The C-terminal acidic residue of At CNIH5 is not required to interact with At PHT1;1, implying that At CNIH5 employs a distinct cargo selection mechanism for At PHT1;1.
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We showed the upregulation of At CNIH5 proteins in the Pi-limited root and in the Pi-replete root of the Pi overaccumulator pho2 . As increasing in-situ At CNIH5 expression/activity enhances plant growth, we propose that At CNIH5 functions as a low Pi-responsive hub, facilitating the ER export of specific membrane cargoes and thereby improving plant fitness under suboptimal Pi availability and promoting agricultural sustainability.
Synopsis
Arabidopsis thaliana CORNICHON HOMOLOG 5 ( At CNIH5) acts as a low phosphate (Pi)-responsive hub that controls efficient ER export of specific membrane cargoes beyond PHT1 Pi transporters to improve plant fitness under suboptimal Pi availability. Unlike the fungal and rice CNIHs interacting with their cognate cargoes through the C-terminal acidic motif, At CNIH5 employs a distinct cargo selection mechanism for At PHT1;1.
