Table 1. Variable Importance for the Projection (VIP) for each discriminant protein that separates ozone fumigated poplar leaves (O) from control leaves (C) in the OPLS model.
| Functionalcategory | Accession | VIP score | SE | Description | Function (MapManBIN) | Log2 (O/C) |
| Decrease in S-nitrosylation after ozone | ||||||
| Amino acid+ Protein | POPTR_0017s10920.1 | 1.721 | 0.797 | Cyclophylin-type protein | Protein/folding | −1.3* |
| POPTR_0021s00380.1 | 1.256 | 1.202 | T-protein of glycine decarboxylasecomplex | Amino acid metabolism/degradation | −0.6 | |
| Photosynthesis | POPTR_0001s13800.1 | 1.997 | 0.513 | Chlorophyll a/b-binding protein 2precursor | Photosynthesis/lightreaction | −2.5** |
| POPTR_0015s07340.1 | 1.955 | 0.591 | Chlorophyll a/b-binding protein 4 | Photosynthesis/lightreaction | −2.3** | |
| POPTR_0005s26080.1 | 1.896 | 0.510 | Chlorophyll a/b-binding protein 2 | Photosynthesis/lightreaction | −1.6** | |
| POPTR_0001s11600.1 | 1.745 | 0.702 | Photosystem I reaction centersubunit III | Photosynthesis/lightreaction | −1.4* | |
| POPTR_0019s09140.1 | 1.738 | 0.827 | Chlorophyll a/b-binding protein CP26 | Photosynthesis/lightreaction | −1.5* | |
| POPTR_0011s02770.1 | 1.710 | 0.998 | Chlorophyll a/b-binding protein 2 | Photosynthesis/lightreaction | −3.7* | |
| POPTR_0010s22790.1 | 1.669 | 0.952 | Chlorophyll a/b-binding protein,putative | Photosynthesis/lightreaction | −3.5* | |
| POPTR_0008s15100.1 | 1.627 | 1.103 | Photosystem I 20 kD protein | Photosynthesis/lightreaction | −0.5* | |
| POPTR_0008s06720.1 | 1.288 | 1.213 | Chlorophyll a/b-binding protein | Photosynthesis/lightreaction | −0.8 | |
| Primary Metabolism | POPTR_0018s07380.1 | 1.760 | 0.874 | Sucrose synthase | Major CHO metabolism/degradation | −3.0* |
| POPTR_0018s09380.1 | 1.697 | 1.007 | Malate dehydrogenase | TCA | −1.3* | |
| POPTR_0012s09570.1 | 1.593 | 1.091 | Glyceraldehyde-3-phosphatedehydrogenase | Glycolysis | −0.6* | |
| POPTR_0008s05640.1 | 1.233 | 1.229 | Triosephosphate isomerase, cytosolic | Glycolysis | −0.7 | |
| Secondary Metabolism | POPTR_0012s00670.1 | 1.877 | 0.817 | Caffeic acid 3-O-methyltransferase | Secondary metabolism/phenylpropanoids | −3.4** |
| POPTR_0008s03810.1 | 1.644 | 1.107 | Phenylalanine ammonia-lyase 2 | Secondary metabolism/phenylpropanoids | −3.6* | |
| POPTR_0001s39630.1 | 1.415 | 1.222 | Polyphenol oxidase | Secondary metabolism | −2.0 | |
| Stress | POPTR_0019s12370.1 | 2.010 | 0.496 | EP3 chitinase | Stress/biotic | −4.7** |
| POPTR_0018s10490.1 | 1.922 | 0.775 | Thaumatin, pathogenesis-relatedprotein | Stress/abiotic | −3.8** | |
| Structural Function | POPTR_0016s02620.1 | 1.696 | 0.805 | Alpha-N-arabinofuranosidase | Cell wall | −1.0* |
| Redox + Signaling | POPTR_0006s11570.1 | 1.774 | 1.004 | Monodehydroascorbate reductase | Redox/ascorbate and glutathione | −0.7* |
| POPTR_0004s10120.1 | 1.570 | 1.172 | Multifunctional chaperone (14-3-3family) | Signaling | −0.3* | |
| Other | POPTR_0018s09580.1 | 1.622 | 1.146 | GDSL-like lipase/acylhydrolase | Misc/GDSL-motif lipase | −1.1* |
| Not Assigned | POPTR_0005s17350.1 | 1.777 | 0.978 | Ascorbate peroxidase, putative | Not assigned | −0.9* |
| POPTR_0005s22860.1 | 1.627 | 1.106 | Aldo/keto reductase family protein | Not assigned | −0.8* | |
| POPTR_0002s05640.1 | 1.518 | 1.148 | Aldo/keto reductase family protein | Not assigned | −1.0* | |
| Increase in S-nitrosylation after ozone | ||||||
| Amino acid+ Proteins | POPTR_0002s12130.1 | 1.824 | 0.889 | Aconitase | Protein/degradation | 1.0** |
| POPTR_0003s20870.1 | 1.640 | 1.017 | Chaperonin precursor | Protein/folding | 1.6* | |
| Photosynthesis | POPTR_0007s07680.1 | 1.623 | 1.062 | Porphobilinogen deaminase | Tetrapyrrole synthesis | 2.6* |
| POPTR_0003s08760.1 | 1.595 | 1.050 | Glycine cleavage system protein H precursor | Photosynthesis/photorespiration | 1.4* | |
| POPTR_0015s07330.1 | 1.528 | 1.066 | Ribulose-phosphate 3-epimerase | Photosynthesis/calvincycle | 1.0* | |
| POPTR_0014s11580.1 | 1.427 | 1.300 | CP12 domain-containing protein | Photosynthesis/calvincycle | 1.9 | |
| Primary Metabolism | POPTR_0006s03660.1 | 1.583 | 1.151 | Glutamate synthase, ferredoxin-dependent | N-metabolism | 1.3* |
| POPTR_0016s03630.1 | 1.434 | 1.275 | Glutamate synthase, ferredoxin-dependent | N-metabolism | 1.9 | |
| Redox+ Signaling | POPTR_0001s22980.1 | 1.848 | 0.869 | Calmodulin-like protein 6a | Signaling/calcium | 2.9** |
| POPTR_0013s10250.1 | 1.586 | 1.077 | Peroxiredoxin 5, putative | Redox | 0.8* | |
| POPTR_0002s08260.1 | 1.416 | 1.110 | Protein disulfide-isomerase,precursor | Redox | 0.7 | |
| Structural Function | POPTR_0001s29670.1 | 1.611 | 1.055 | Tubulin alpha chain | Cell/organisation | 1.1* |
| Other | POPTR_0001s23310.1 | 1.386 | 1.226 | Glycosyl hydrolase familyprotein | Misc/gluco-, galacto- andmannosidases | 1.0 |
Proteins showing VIP >1 and uncertainty bars of jack-knifing method (SE) < than the respective VIP value were defined as discriminant proteins. Additionally, discriminant proteins were tested for significance difference (P<0.05) between C and O plants independently from multivariate data analysis using t-test (* = P<0.05; ** = P<0.01) applying a FDR of 5%. Log fold changes (ozone/control) were calculated from normalized protein abundances (Table S1C). Annotation and functional categorization was obtained from Phytozome and PPDB (http://www.phytozome.net/; http://ppdb.tc.cornell.edu/dbsearch/searchacc.aspx).