Overlapping and antagonistic activities of BASIC PENTACYSTEINE genes affect a range of developmental processes in Arabidopsis.

The BASIC PENTACYSTEINE (BPC) proteins are a plant-specific transcription factor family that is present throughout land plants. The Arabidopsis BPC proteins have been categorized into three classes based on sequence similarity, and we demonstrate that there is functional overlap between classes. Single gene mutations produce no visible phenotypic effects, and severe morphological phenotypes occur only in higher order mutants between members of classes I and II, with the most severe phenotype observed in bpc1-1 bpc2 bpc4 bpc6 plants. These quadruple mutants are dwarfed and display small curled leaves, aberrant ovules, altered epidermal cells and reduced numbers of lateral roots. Affected processes include coordinated growth of cell layers, cell shape determination and timing of senescence. Disruption of BPC3 function rescues some aspects of the bpc1-1 bpc2 bpc4 bpc6 phenotype, indicating that BPC3 function may be antagonistic to other members of the family. Ethylene response is diminished in bpc1-1 bpc2 bpc4 bpc6 plants, although not all aspects of the phenotype can be explained by reduced ethylene sensitivity. Our data indicate that the BPC transcription factor family is integral for a wide range of processes that support normal growth and development.