plastids undifferentiated, a nuclear mutation that disrupts plastid differentiation in Zea mays L.

Photosynthetic development in any plant requires the intracellular co-ordin ation of chloroplast and nuclear gene expression programs. In this report, we investigate the role of a nuclear gene in photosynthetic development by examining C-4 photosynthetic differentiation in a yellow mutant of maize (Z ea mays L.). The plastids undifferentiated (pun) mutation disrupts plastid biogenesis in both bundle sheath and mesophyll cells, at an early developme ntal stage and in a light-independent manner. Chloroplast thylakoids are di srupted in the mutant and both membrane-associated and soluble chloroplast- encoded proteins accumulate at much reduced levels. The observed plastid mo rphology is consistent with a general defect in chloroplast biogenesis that is most likely exerted at the post-translational level. Despite aberrant c hloroplast development, nuclear photosynthetic genes are expressed normally in pun mutants. Thus, neither functional chloroplasts nor the Pun gene pro duct are required to establish nuclear photosynthetic gene expression patte rns in maize.