Cell wall invertase activity regulates the expression of the transfer cell-specific transcription factor ZmMRP-1.

MAIN CONCLUSION: Studies in cell wall bound invertase mutants indicate that the promoter of the transfer cell-specific transcription factor, ZmMRP - 1 , is modulated by the carbohydrate balance. Transfer cells are highly specialized plant cells located at the surfaces that need to support an intensive exchange of nutrients, such as the entrance of fruits, seeds and nodules or the young branching points along the stem. ZmMRP-1 is a one-domain MYB-related transcription factor specifically expressed at the transfer cell layer of the maize endosperm. Previous studies demonstrated that this factor regulates the expression of a large number of transfer cell-specific genes, and suggested that ZmMRP-1 is a key regulator of the differentiation of this tissue. The expression of this gene is largely dominated by positional cues, but within the ZmMRP-1 expressing cells the promoter appears to be modulated by sugars. Here we have investigated in vivo this modulation. Using maize and Arabidopsis mutants for cell wall invertase genes, we found that the absence of cell wall invertase activity is a major inductive signal of the ZmMRP-1 expression.