Camouflage Patterning in Maize Leaves Results from a Defect in Porphobilinogen Deaminase

Maize leaves are produced from polarized cell divisions that result in clonal cell lineages arrayed along the long axis of the leaf. We utilized this stereotypical division pattern to identify a collection of mutants that form chloroplast pigmentation sectors that violate the clonal cell lineages. Here, we describe the camouflage1 (cf1) mutant, which develops nonclonal, yellow-green sectors in its leaves. We cloned the cf1 gene by transposon tagging and determined that it encodes porphobilinogen deaminase (PBGD), an enzyme that functions early in chlorophyll and heme biosynthesis. While PBGD has been characterized biochemically, no viable mutations in this gene have been reported in plants. To investigate the in vivo function of PBGD, we characterized the cf1 mutant. Histological analyses revealed that cf1 yellow sectors display the novel phenotype of bundle sheath cell-specific death. Light-shift experiments determined that constant light suppressed cf1 sector formation, a dark/light transition is required to induce yellow sectors, and that sectors form only during a limited time of leaf development. Biochemical experiments determined that cf1 mutant leaves have decreased PBGD activity and increased levels of the enzyme substrate in both green and yellow regions. Furthermore, the cf1 yellow regions displayed a reduction in catalase activity. A threshold model is hypothesized to explain the cf1 variegation and incorporates photosynthetic cell differentiation, reactive oxygen species scavenging, and PBGD function.