Required for methylation of the 3' adenosines in the small subunit of plastid rRNA. Essential for chloroplast biogenesis at low temperatures. No visible phenotype when grown at 22 degrees Celsius. Chilling-induced chlorosis and reduced growth at 5 degrees Celsius. Belongs to the class I-like SAM-binding methyltransferase superfamily. rRNA adenine N(6)-methyltransferase family.