Nuclear genome-encoded factor involved in ribosome biogenesis in chloroplasts (PubMed:22576849, PubMed:23227895, PubMed:25043599). Binds specific group II introns in chloroplasts and facilitates their splicing. Is required for rRNA maturation in plastids and may contribute to the assembly of the large (50S) ribosomal subunit (PubMed:22576849). Required for normal development of chloroplasts (PubMed:22576849, PubMed:23227895, PubMed:25043599). Required for the expression of transcripts encoding plastid-localized enzymes involved in abscisic acid (ABA) biosynthesis. Required for maintenance of ABA levels and response to salt stress (PubMed:23227895). Possesses RNA chaperone activity for proper splicing of introns in chloroplasts. Essential for chloroplast function and abiotic stress responses (PubMed:25043599). ATP + H2O = ADP + H(+) + phosphate Highly expressed in young seedlings. The Q motif is unique to and characteristic of the DEAD box family of RNA helicases and controls ATP binding and hydrolysis. Embryonic lethality when homozygous. Plants with the weak allele rh3-4 exhibits albino cotyledons, pale green leaf phenotype, slow growth, short petioles, small leaves, reduced content of chlorophyll, altered structure of chloroplast ribosomes and reduced levels of chloroplast proteins. Belongs to the DEAD box helicase family. DDX21/DDX50 subfamily.