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

SUMMARYThe BASIC PENTACYSTEINE (BPC) proteins are a plant-specific transcription factor family that is presentthroughout land plants. The Arabidopsis BPC proteins have been categorized into three classes based onsequence similarity, and we demonstrate that there is functional overlap between classes. Single genemutations produce no visible phenotypic effects, and severe morphological phenotypes occur only in higherorder mutants between members of classes I and II, with the most severe phenotype observed in bpc1-1 bpc2bpc4 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 growthof cell layers, cell shape determination and timing of senescence. Disruption of BPC3 function rescues someaspects of the bpc1-1 bpc2 bpc4 bpc6 phenotype, indicating that BPC3 function may be antagonistic to othermembers of the family. Ethylene response is diminished in bpc1-1 bpc2 bpc4 bpc6 plants, although not allaspects of the phenotype can be explained by reduced ethylene sensitivity. Our data indicate that the BPCtranscription factor family is integral for a wide range of processes that support normal growth anddevelopment.Keywords: transcription factor, barley B recombinant, BASIC PENTACYSTEINE, Arabidopsis, development,GAGA-binding factor.INTRODUCTIONGene regulation is essential to the growth and survival oforganisms, and transcription factors play a central role inthis process. In Arabidopsis, more than 1900 loci have beenclassified into 64 transcription factor families (Guo et al.,2005). Members of a gene family may have unique orredundant activities, with diverged sequences within afamily more likely to have divergent activities. One poorlyunderstood plant-specific transcription factor family isthe BARLEY B RECOMBINANT/BASIC PENTACYSTEINE(BBR/BPC) family. The BBR/BPC genes are presentthroughout the land plants, and members of the BBR/BPCprotein family from Glycine max (soybean), Hordeumvulgare (barley) and Arabidopsis have been shown to bindspecific DNA sequences (Kooiker et al., 2005; Meister et al.,2004; Sangwan and O’Brian, 2002; Santi et al., 2003).A soybean member of this family, the GAGA BINDINGPROTEIN (GBP), specifically bound a (GA)