The genes coding for the core metabolic enzymes of the photorespiratory pathway that allows plants with C3-type photosynthesis
to survive in an oxygen-rich atmosphere, have been largely discovered in genetic screens aimed to isolate mutants that are unviable
under ambient air. As an exception, glycolate oxidase (GOX) mutants with a photorespiratory phenotype have not been described
yet in C3 species. Using Arabidopsis (Arabidopsis thaliana) mutants lacking the peroxisomal CATALASE2 (cat2-2) that display
stunted growth and cell death lesions under ambient air, we isolated a second-site loss-of-function mutation in GLYCOLATE
OXIDASE1 (GOX1) that attenuated the photorespiratory phenotype of cat2-2. Interestingly, knocking out the nearly identical GOX2
in the cat2-2 background did not affect the photorespiratory phenotype, indicating that GOX1 and GOX2 play distinct metabolic
roles.We further investigated their individual functions in single gox1-1 and gox2-1 mutants and revealed that their phenotypes can
be modulated by environmental conditions that increase the metabolic flux through the photorespiratory pathway. High light
negatively affected the photosynthetic performance and growth of both gox1-1 and gox2-1 mutants, but the negative consequences
of severe photorespiration were more pronounced in the absence of GOX1, which was accompanied with lesser ability to process
glycolate. Taken together, our results point toward divergent functions of the two photorespiratory GOX isoforms in Arabidopsis
and contribute to a better understanding of the photorespiratory pathway.
Supplemental Figure S1. GOX1 and GOX2 gene models.
Supplemental Figure S2. Read coverage of GOX1 and GOX2 loci from
RNA-seq analysis of cat2-2 gox1-1, cat2-2, and cat2-2 gox2-1 mutants.
Supplemental Figure S3. Heat map of differentially expressed transcripts
(|log2 FC| . 1, FDR , 0.05) between cat2-2 gox1-1, cat2-2 gox2-1, and
cat2-2 mutants under control high CO2 conditions aimed at inhibiting
the photorespiratory flux.
Supplemental Figure S4. Redox status of Col-0, cat2-2, cat2-2 gox1-1, and
cat2-2 gox2-1 plants grown under ambient air and moderate light intensity
(300 mmol m22 s
Supplemental Figure S5. Nonphotochemical quenching and phosphorylation
of LHCBII upon exposure of Col-0, gox1-1, and gox2-1 plants grown
under conditions limiting photorespiration to high light.
Supplemental Figure S6. GOX1 and GOX2 genes in Brassicaceae are clustered
as monophyly in the gene tree of ORTHO03D000507 from PLAZA
Supplemental Figure S8. GOX1 and GOX2 transcript abundance.
Supplemental Table S1. Maximum likelihood estimates of parameters under
branch models on both postduplication branches leading to the
GOX1 and GOX2 clades.
Supplemental Table S2. Likelihood ratio tests for comparing different
branch models applied to both postduplication branches leading to the
GOX1 and GOX2 clades.
Supplemental Table S3. The modified branch-site models for detecting
positive selection on six branches after the duplication event leading
to GOX2 in Arabidopsis.
Supplemental Table S4. List of primers used in this study.
Supplemental Table S5. Mutations enriched in line 238.3.
Supplemental Table S6. Data sources and sequence accessions.
Supplemental Data Set 1. RNA-seq results.
Supplemental Data Set 2. List of transcripts that responded to the photorespiratory
stress treatment in a genotype-specific manner.
Supplemental Data Set 3. Gene Set Enrichment Analysis (http://
structuralbiology.cau.edu.cn/PlantGSEA) of the transcripts that responded
to the photorespiratory stress treatment in a genotype-specific