NORMAL GENOMIC

• Wang MY et al.
• The cotton transcription factor TCP14 functions in auxin-mediated epidermal cell differentiation and elongation.
• Plant Physiol. 2013; 162: 1669-80
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• Plant-specific TEOSINTE-BRANCHED1/CYCLOIDEA/PCF (TCP) transcription factors play crucial roles in development, but their functional mechanisms remain largely unknown. Here, we characterized the cellular functions of the class I TCP transcription factor GhTCP14 from upland cotton (Gossypium hirsutum). GhTCP14 is expressed predominantly in fiber cells, especially at the initiation and elongation stages of development, and its expression increased in response to exogenous auxin. Induced heterologous overexpression of GhTCP14 in Arabidopsis (Arabidopsis thaliana) enhanced initiation and elongation of trichomes and root hairs. In addition, root gravitropism was severely affected, similar to mutant of the auxin efflux carrier PIN-FORMED2 (PIN2) gene. Examination of auxin distribution in GhTCP14-expressing Arabidopsis by observation of auxin-responsive reporters revealed substantial alterations in auxin distribution in sepal trichomes and root cortical regions. Consistent with these changes, expression of the auxin uptake carrier AUXIN1 (AUX1) was up-regulated and PIN2 expression was down-regulated in the GhTCP14-expressing plants. The association of GhTCP14 with auxin responses was also evidenced by the enhanced expression of auxin response gene IAA3, a gene in the AUXIN/INDOLE-3-ACETIC ACID (Aux/IAA) family. Electrophoretic mobility shift assays showed that GhTCP14 bound the promoters of PIN2, IAA3, and AUX1, and transactivation assays indicated that GhTCP14 had transcription activation activity. Taken together, these results demonstrate that GhTCP14 is a dual-function transcription factor able to positively or negatively regulate expression of auxin response and transporter genes, thus potentially acting as a crucial regulator in auxin-mediated differentiation and elongation of cotton fiber cells.

• Frigerio M et al.
• Transcriptional regulation of gibberellin metabolism genes by auxin signaling in Arabidopsis.
• Plant Physiol. 2006; 142: 553-63
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• Auxin and gibberellins (GAs) overlap in the regulation of multiple aspects of plant development, such as root growth and organ expansion. This coincidence raises questions about whether these two hormones interact to regulate common targets and what type of interaction occurs in each case. Auxins induce GA biosynthesis in a range of plant species. We have undertaken a detailed analysis of the auxin regulation of expression of Arabidopsis (Arabidopsis thaliana) genes encoding GA 20-oxidases and GA 3-oxidases involved in GA biosynthesis, and GA 2-oxidases involved in GA inactivation. Our results show that auxin differentially up-regulates the expression of various genes involved in GA metabolism, in particular several AtGA20ox and AtGA2ox genes. Up-regulation occurred very quickly after auxin application; the response was mimicked by incubations with the protein synthesis inhibitor cycloheximide and was blocked by treatments with the proteasome inhibitor MG132. The effects of auxin treatment reflect endogenous regulation because equivalent changes in gene expression were observed in the auxin overproducer mutant yucca. The results suggest direct regulation of the expression of GA metabolism genes by Aux/IAA and ARF proteins. The physiological relevance of this regulation is supported by the observation that the phenotype of certain gain-of-function Aux/IAA alleles could be alleviated by GA application, which suggests that changes in GA metabolism mediate part of auxin action during development.

• de Pater S, Pham K, Memelink J, Kijne J
• RAP-1 is an Arabidopsis MYC-like R protein homologue, that binds to G-box sequence motifs.
• Plant Mol Biol. 1997; 34: 169-74
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• An Arabidopsis cDNA clone encoding a DNA-binding protein, RAP-1, was isolated by southwestern screening of an Escherichia coli cDNA expression library. The protein contains a bHLH DNA-binding domain and is homologous to R proteins, regulating anthocyanin biosynthesis. RAP-1 binds to the sequence CACNTG. It is encoded by a single gene, which is expressed to high levels in root and stem and to low levels in leaf and flower. No expression could be detected in siliques. Rap-1 does not correspond to one of the known loci involved in anthocyanin biosynthesis, since it is located at a different map position. In contrast to the maize R protein Lc, RAP-1 did not induce anthocyanin biosynthesis in pea cotyledons. Thus, RAP-1 is a novel member of the bHLH class of DNA-binding proteins.