A negative regulatory role for auxin in sulphate deficiency response in Arabidopsis thaliana
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Sulphate is a major macronutrient required for the synthesis of the sulphur (S)-containing amino acid cysteine and thus is critical for cellular metabolism, growth and development and response to various abiotic and biotic stresses. A recent genome-wide expression study suggested that several auxin-inducible genes were up-regulated by S deficiency in Arabidopsis. Here, we examined the relationship between auxin signaling and S deficiency. Investigation of DR5::GUS expression patterns indicates that auxin accumulation and/or response is suppressed by S deficiency. Consistently, S deficiency resulted in the suppression of lateral root development, but the axr1-3 mutant was insensitive to this response. Furthermore, the activation of the promoter for the putative thioglucosidase gene (At2g44460) by S deficiency was suppressed by auxin, cytokinin and abscisic acid (ABA). Interestingly, the activation of At2g44460 by S deficiency is regulated by the availability of carbon and nitrogen nutrients in a tissue-specific manner. These results demonstrate that auxin plays a negative role in signaling to S deficiency. Given that activation of the genes encoding the sulphate transporter SULTR1;2 and 5′-adenylylsulphate reductase APR2 are suppressed by cytokinin only, we hypothesize that while cytokinin may play an important role in general S deficiency response, auxin might be only involved in a subset of S deficiency responses such as the release of thiol groups from the S storage sources.
KeywordsSulphate deficiency Sulfur metabolism Thioglucosidase APR2 Auxin axr1
This work was supported by the NIH-SCORE grant (S06GM008225, Project Number 12 to Z-L Z) and in part by the City University of New York and the PSC-CYNY program (68436-00-37 to Z-L Z). We are grateful to Haiyang Wang (Boyce Thompson Institute) for providing the axr1-3 seeds, Erwin Grill (Tubingen University) for the pRD29B::GUS line, and Zhenbiao Yang (University of California at Riverside) for the DR5::GUS line with the permission of the use from Thomas Guilfoyle (University of Missouri-Columbia). We thank members of the Zheng Laboratory at the CUNY Lehman College for helpful discussion and technical assistance. We appreciate David Cain (CUNY Lehman College) for assistance with plant growth. We also thank anonymous reviewers for their constructive comments.
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