S-sulfocysteine synthase that plays an important role in chloroplast function and is essential for light-dependent redox regulation and photosynthetic performance within the chloroplast (PubMed:20179139, PubMed:22829322, PubMed:23333972). Probably unable to interact with SAT and to form the decameric Cys synthase complex (CSC) required for O-acetylserine (thiol)-lyase (OAS-TL) enzymatic activity (PubMed:18223034). Lacks OAS-TL activity (PubMed:20179139). O-acetyl-L-serine + thiosulfate = acetate + H(+) + S-sulfo-L-cysteine Optimum pH is 8-9. Optimum temperature is 30 degrees Celsius. Homodimer. No visible phenotype under normal growth condition (PubMed:18024555). No visible phenotype under short day (SD) conditions (PubMed:20179139). Reduced growth and pale green leaf phenotype under long day (LD) conditions (PubMed:20179139, PubMed:22829322). Belongs to the cysteine synthase/cystathionine beta-synthase family.