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Tryptophan-dependent auxin biosynthesis is required for HD-ZIP III-mediated xylem patterning
Robertas Ursache1, Shunsuke Miyashima, Qingguo Chen
1Institute of Biotechnology, Department of Bio and Environmental Sciences, University of Helsinki, FIN-00014, Finland.
Development (Cambridge, England)
|March 6, 2014
Summary
Auxin biosynthesis, not just transport, is crucial for plant xylem development. This study reveals that auxin production in roots promotes the formation of metaxylem, essential for water and mineral transport in plants.
Area of Science:
- Plant Biology
- Molecular Biology
- Developmental Biology
Background:
- Plant vascular development relies on xylem for water and mineral transport.
- In Arabidopsis roots, xylem development involves distinct metaxylem and protoxylem cell fates.
- Class III HD-ZIP transcription factors regulate xylem cell identity, with high and low expression promoting metaxylem and protoxylem, respectively.
Purpose of the Study:
- To identify factors promoting high HD-ZIP III expression for metaxylem identity.
- To investigate the role of auxin biosynthesis in metaxylem specification.
- To elucidate the combined roles of auxin transport and biosynthesis in establishing the xylem axis.
Main Methods:
- Analysis of auxin biosynthesis gene expression in Arabidopsis root vascular tissue.
- Phenotypic analysis of auxin biosynthesis mutants (trp2-12, wei8 tar2, quintuple yucca mutant).
- Assessment of metaxylem development in plants treated with L-kynurenine, an auxin biosynthesis inhibitor.
- Complementation analysis using synthetically elevated HD-ZIP III expression.
Main Results:
- Auxin biosynthesis genes are expressed in outer root layers surrounding vascular tissue.
- Mutations in auxin biosynthesis genes or inhibition of auxin biosynthesis lead to downregulated HD-ZIP III expression and defects in metaxylem development.
- Elevated HD-ZIP III expression can partially rescue patterning defects in auxin biosynthesis mutants.
Conclusions:
- Root-based auxin biosynthesis is essential for promoting HD-ZIP III expression and specifying metaxylem identity.
- Polar auxin transport alone is insufficient for proper xylem axis formation; auxin biosynthesis is additionally required.
- This study highlights a novel role for auxin biosynthesis in regulating plant vascular development.
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