*4.3. Sequencing of the cDNA Encoding the GOX from Spirogyra Pratensis*

The complete sequence of the *Spirogyra* GOX was extracted from an existing Expressed sequence tag (EST) library [72], which was screened via BLASTX using the *Arabidopsis* At-GOX2 (At3g14415) sequence. The full-length cDNA sequence from *Spirogyra* (Figure S2) was compared to known GOX and LOX proteins, and checked for completeness. The sequence of *Spirogyra* GOX (Sp-GOX) was deposited in GenBank under the accession number AVP27295.1.

#### *4.4. Estimation and Synthesis of the cDNA Encoding the GOX from Cyanophora Paradoxa*

The GOX sequence from *C. paradoxa* was identified by BLAST searches with plant and algal GOX proteins. The originally annotated *Cyanophora* protein of the genomic Contig54585 consists of 316 amino acids, which is considerably shorter than the GOX protein from *Arabidopsis* (367 amino acids). Initially, we used this cDNA to synthesize the *Cyanophora gox* gene; however, we failed to obtain an enzymatic active protein, most likely because of the missing C-terminus. Subsequent BLAST searches including EST sequences identified two different EST sequences (EG947183.1 and ES232585.1), which partially overlap with the *gox* gene in the *Cyanophora* genome database (Contig54585; http://cyanophora.rutgers.edu/cyanophora/home.php). The newly obtained cDNA for the *Cyanophora gox* gene (348 amino acids long, sequence called Cp-GOXb) was also used for gene synthesis (Thermo Fisher), but we again failed to produce an enzymatic active protein. Finally, we re-sequenced the entire *gox* gene from *Cyanophora* gDNA using new primer sets (CpGOXb\_275\_fw, CpGOXb\_369\_fw, and CpGOXb\_655\_rv; Table S3). The new sequence revealed a missing 15-nucleotides-long insertion in the originally annotated genomic version of this *gox* gene. The final cDNA sequence gave rise to the corrected protein, which was named Cp-GOXc. The entire gene was synthesized by PCR using the DNA of the previously obtained expression vector pASG-IBA43plus-*cp*-*goxb* as a template and the phosphorylated primers CpGOX\_RV\_5P and CpGOX\_FW\_5P (Table S3). The previously 15 missing

bases coding for five amino acids were included via the used primer. After the ligation of the final PCR product, we obtained the expression vector pASG-IBA43plus-*cp*-*goxc* harboring the correct cDNA sequence of the *gox* gene from *Cyanophora*. A scheme including all steps leading to the corrected *gox* gene from *Cyanophora* is shown in Figure S7.
