LIGHT-DEPENDENT SPATIAL AND TEMPORAL EXPRESSION OF PIGMENT REGULATORYGENES IN DEVELOPING MAIZE SEEDS

Both light and developmental stimuli are directly involved in the regu lation of plant gene expression. In maize, activation of the anthocyan in pathway represents an excellent model system for studying the inter actions between an external factor, such as light, and internal factor s that regulate plant and seed development. By analyzing in detail the aleurone and pericarp seed layers, different developmental windows fo r tight have been found in the two tissues-the former in the advanced stages of development and the latter in the early stages of seed devel opment. Transcriptional control of the structural genes involved in an thocyanin deposition within the pericarp is known to be exerted by the Sn and pl genes, whereas the aleurone is controlled by the R and C1 r egulatory genes. By using in situ hybridization analysis, we detected tissue-specific expression of Sn and R in the seed layers, revealing a correlation between structural gene activation and anthocyanin accumu lation, In addition, RNA gel blot analysis revealed that Sn expression is enhanced by light, whereas the R gene expression is not. However, the light-induced expression of the myb-type genes C1 and pl, detected by reverse transcriptase-polymerase chain reaction, was found to be t he limiting factor for conferring the developmental competence of the pericarp and the aleurone layers to light responsiveness.