Auxin and ethylene induce flavonol accumulation through distinct transcriptional networks.
ABSTRACT Auxin and ethylene are key regulators of plant growth and development, and thus the transcriptional networks that mediate responses to these hormones have been the subject of intense research. This study dissected the hormonal cross talk regulating the synthesis of flavonols and examined their impact on root growth and development. We analyzed the effects of auxin and an ethylene precursor on roots of wild-type and hormone-insensitive Arabidopsis (Arabidopsis thaliana) mutants at the transcript, protein, and metabolite levels at high spatial and temporal resolution. Indole-3-acetic acid (IAA) and 1-aminocyclopropane-1-carboxylic acid (ACC) differentially increased flavonol pathway transcripts and flavonol accumulation, altering the relative abundance of quercetin and kaempferol. The IAA, but not ACC, response is lost in the transport inhibitor response1 (tir1) auxin receptor mutant, while ACC responses, but not IAA responses, are lost in ethylene insensitive2 (ein2) and ethylene resistant1 (etr1) ethylene signaling mutants. A kinetic analysis identified increases in transcripts encoding the transcriptional regulators MYB12, Transparent Testa Glabra1, and Production of Anthocyanin Pigment after hormone treatments, which preceded increases in transcripts encoding flavonoid biosynthetic enzymes. In addition, myb12 mutants were insensitive to the effects of auxin and ethylene on flavonol metabolism. The equivalent phenotypes for transparent testa4 (tt4), which makes no flavonols, and tt7, which makes kaempferol but not quercetin, showed that quercetin derivatives are the inhibitors of basipetal root auxin transport, gravitropism, and elongation growth. Collectively, these experiments demonstrate that auxin and ethylene regulate flavonol biosynthesis through distinct signaling networks involving TIR1 and EIN2/ETR1, respectively, both of which converge on MYB12. This study also provides new evidence that quercetin is the flavonol that modulates basipetal auxin transport.
Plant Science 02/2013; · 2.94 Impact Factor
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ABSTRACT: Phenolics are antioxidants present in tomato fruit that confer healthy benefits and exhibit crucial roles for plant metabolism and response to environmental stimuli. An approach based on two genomics platforms was undertaken to identify candidate genes associated to higher phenolics content in tomato fruit. A comparative transcriptomic analysis between the S. pennellii Introgression Line 7-3, which produced an average higher level of fruit phenolics, and the cultivated variety M82, revealed that their differences are attributed to genes involved in phenolics accumulation into the vacuole. The up-regulation of genes coding for one MATE-transporter, one vacuolar sorting protein and three GSTs supported this hypothesis. The observed balancing effect between two ethylene responsive factors (ERF1 and ERF4) was also hypothesized to drive the transcriptional regulation of these transport genes. In order to confirm such model a TILLING platform was explored. A mutant was isolated harbouring a point mutation in the ERF1 cds that affects the protein sequence and its expected function. Fruits of the mutant exhibited a significant reduced level of phenolics than the control variety. Changes in the expression of genes involved in sequestration of phenolics in vacuole also supported the hypothesized key-role of ERF1 in orchestrating these genes.Plant Science 05/2013; 205-206:87-96. · 2.94 Impact Factor