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The WIP family of transcription factors comprises the A1d subgroup of C2H2 zinc finger proteins. This family has six members in Arabidopsis thaliana and most of the known functions have been described by analyzing single knockout mutants. However, it has been shown that WIP2 and its closest paralogs WIP4 and WIP5 have a redundant and essential function in root meristems. It is likely that these and other WIP genes perform more, still unknown, functions. To obtain hints about these other functions, the expression of the six WIP genes was explored. Moreover, phenotypic ana-lyses of overexpressors and wip mutants revealed functions in modulating organ and cell size, stomatal density, and vasculature development. [ABSTRACT FROM AUTHOR]

The Arabidopsis thaliana transparent testa 1 gene codes for a nuclear protein and controls sead coat endothelium development. Data reveal that the protein contains a combination of two TFIIIA-type zinc finger motifs, termed WIP, and WIP genes regulate endothelium differentiation.

The gynoecium, the female reproductive part of the flower, is key for plant sexual reproduction. During its development, inner tissues such as the septum and the transmitting tract tissue, important for pollen germination and guidance, are formed. In Arabidopsis, several transcription factors are known to be involved in the development of these tissues. One of them is NO TRANSMITTING TRACT (NTT), essential for transmitting tract formation. We found that the NTT protein can interact with several gynoecium-related transcription factors, including several MADS-box proteins, such as SEEDSTICK (STK), known to specify ovule identity. Evidence suggests that NTT and STK control enzyme and transporterencoding genes involved in cell wall polysaccharide and lipid distribution in gynoecial medial domain cells. The results indicate that the simultaneous loss of NTT and STK activity affects polysaccharide and lipid deposition and septum fusion, and delays entry of septum cells to their normal degradation program. Furthermore, we identified KAWAK, a direct target of NTT and STK, which is required for the correct formation of fruits in Arabidopsis. These findings position NTT and STK as important factors in determining reproductive competence. [ABSTRACT FROM AUTHOR]

Petunia mutants ( Petunia hybrida) with blue flowers defined a novel vacuolar proton pump consisting of two interacting P- ATPases, PH1 and PH5, that hyper-acidify the vacuoles of petal cells. PH5 is similar to plasma membrane H+P3A- ATPase, whereas PH1 is the only known eukaryoticP3B- ATPase. As there were no indications that this tonoplast pump is widespread in plants, we investigated the distribution and evolution of PH1 and PH5., We combined database mining and phylogenetic and synteny analyses of PH1- and PH5-like proteins from all kingdoms with functional analyses (mutant complementation and intracellular localization) of homologs from diverse angiosperms., We identified functional PH1 and PH5 homologs in divergent angiosperms. PH5 homologs evolved from plasma membrane P3A- ATPases, acquiring an N-terminal tonoplast-sorting sequence and new cellular function before angiosperms appeared. PH1 is widespread among seed plants and related proteins are found in some groups of bacteria and fungi and in one moss, but is absent in most algae, suggesting that its evolution involved several cases of gene loss and possibly horizontal transfer events., The distribution of PH1 and PH5 in the plant kingdom suggests that vacuolar acidification by P- ATPases appeared in gymnosperms before flowers. This implies that, next to flower color determination, vacuolar hyper-acidification is required for yet unknown processes. [ABSTRACT FROM AUTHOR]

Intracellular pH homeostasis is essential for all living cells. In plants, pH is usually maintained by three structurally distinct and differentially localized types of proton pump: P-type H+- ATPases in the plasma membrane, and multimeric vacuolar-type H+- ATPases (V- ATPases) and vacuolar H+-pyrophosphatases (H+- PPases) in endomembranes. Here, we show that reduced accumulation of proanthocyanidins ( PAs) and hence the diminished brown seed coloration found in the Arabidopsis thaliana mutant transparent testa 13 ( tt13) is caused by disruption of the gene encoding the P3A- ATPase AHA10. Identification of the gene encoded by the tt13 locus completes the molecular characterization of the classical set of transparent testa mutants. Cells of the tt13 seed coat endothelium do not contain PA-filled central vacuoles as observed in the wild-type. tt13 phenocopies tt12, a mutant that is defective in vacuolar import of the PA precursor epicatechin. Our data show that vacuolar loading with PA precursors depends on TT13. Consistent with the tt13 phenotype, but in contrast to other isoforms of P-type H+- ATPases, TT13 localizes to the tonoplast. PA accumulation in tt13 is partially restored by expression of the tonoplast localized H+- PPase VHP1. Our findings indicate that the P3A- ATPase TT13 functions as a proton pump in the tonoplast of seed coat endothelium cells, and generates the driving force for TT12-mediated transport of PA precursors to the vacuole. [ABSTRACT FROM AUTHOR]

Flavonol synthase (FLS) (EC-number 1.14.11.23), the enzyme that catalyses the conversion of flavonols into dihydroflavonols, is part of the flavonoid biosynthesis pathway. In Arabidopsis thaliana, this activity is thought to be encoded by several loci. In addition to the FLAVONOL SYNTHASE1 (FLS1) locus that has been confirmed by enzyme activity assays, loci displaying similarity of the deduced amino acid sequences to FLS1 have been identified. We studied the putative A. thaliana FLS gene family using a combination of genetic and metabolite analysis approaches. Although several of the FLS gene family members are expressed, only FLS1 appeared to influence flavonoid biosynthesis. Seedlings of an A. thaliana fls1 null mutant ( fls1-2) show enhanced anthocyanin levels, drastic reduction in flavonol glycoside content and concomitant accumulation of glycosylated forms of dihydroflavonols, the substrate of the FLS reaction. By using a leucoanthocyanidin dioxygenase (ldox) fls1-2 double mutant, we present evidence that the remaining flavonol glycosides found in the fls1-2 mutant are synthesized in planta by the FLS-like side activity of the LDOX enzyme. [ABSTRACT FROM AUTHOR]

Abstract: In Arabidopsis thaliana, most mutants impaired in flavonoid accumulation were identified through screens for altered seed pigmentation. Mutations in more than 20 loci have been described that can result in a transparent testa (tt) or tannin deficient seed (tds) phenotype. For some of these mutants it is still unclear if they represent additional loci or if they are allelic to known mutations. In this study, we found that tt17 is allelic to tt11 and tds4 and identified a point mutation in tt17 that affects the gene encoding Leucoanthocyanidin Dioxygenase (LDOX). The mutation results in replacement of a cysteine close to the active site of the enzyme by the hydrophobic amino acid tyrosine. Effects of this mutation on protein structure and activity are discussed in the context of LDOX sequences from various genotypes. Regulation of the LDOX promoter was analyzed and found to be directly controlled by different MYB–BHLH–TTG1 transcription factor complexes containing the BHLH factors EGL3 and TT8. Experiments with single and double loss-of-function mutants identified EGL3 and TT8 as necessary regulators of anthocyanin accumulation in developing A. thaliana seedlings. [Copyright &y& Elsevier]