RNA-binding protein that acts as an RNA chaperone to remodel RNA structure and activates their translation (PubMed:30962391). Required for seed pigmentation (PubMed:21139083). Necessary for chloroplast development and subsequent photosynthetic electron flow, as well as for non-photochemical quenching (NPQ) (PubMed:27462450). Rubisco regulatory factor which regulates the concerted biogenesis of NDH, PSI (including PsaA, PsaB, PsaD, PsaF, PsaL, PsaG, PsaK and NdhH) and Cytb(6)f (including PetA, PetB, PetC and PetD) complexes (PubMed:24053212, PubMed:27462450, PubMed:30962391). Binds specifically to and involved in the post-transcriptional regulation of plastid-encoded mRNAs (e.g. rbcL, petA, petB, petD and Ycf1), thus modulating expression, cellular localization/compartmentalization, and photosynthetic function (PubMed:24053212, PubMed:27462450, PubMed:30962391). Interacts with CRP1 and PRFB3. Present in leaves (at protein level) (PubMed:30962391). Confined to leaf chlorenchyma cells (PubMed:24053212). By light. Pigment defective seeds (PubMed:21139083). Virescent/yellow leaves leading to pale-green seedlings, due to reduced photosynthetic function and disruption of associated signaling networks, later associated with impaired photoautotrophy (PubMed:24053212, PubMed:27462450, PubMed:30962391). Abnormal chloroplast development with disrupted granum-stroma thylakoid membranes and disrupted photosynthetic electron flow (PubMed:27462450). Reduced accumulation of rbcL mRNA and less production of Rubisco large subunit (LSU) (PubMed:24053212). Impaired biogenesis of NDH, PSI (including PsaA, PsaB, PsaD, PsaF, PsaL, PsaG, PsaK and NdhH) and Cytb(6)f (including PetA, PetB, PetC and PetD) complexes; this phenotypes are reversed by Ycf1 overexpression (PubMed:27462450, PubMed:30962391). Inhibited induction of non-photochemical quenching (NPQ) (PubMed:27462450). Structural changes to target RNAs (PubMed:30962391). Belongs to the bacterial ribosomal protein bS1 family.