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Transcriptional and Hormonal Regulation of Gravitropism of Woody Stems in PopulusAuthor(s): Suzanne Gerttula; Matthew S. Zinkgraf; Gloria K. Muday; Daniel R. Lewis; Farid M. Ibatullin; Harry Brumer; Foster Hart; Shawn D. Mansfield; Vladimir Filkov; Andrew Groover
Source: The Plant Cell. 27(10): 2800-2813
Publication Series: Scientific Journal (JRNL)
Station: Pacific Southwest Research Station
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DescriptionAngiosperm trees reorient their woody stems by asymmetrically producing a specialized xylem tissue, tension wood, which exerts a strong contractile force resulting in negative gravitropism of the stem. Here, we show, in Populus trees, that initial gravity perception and response occurs in specialized cells through sedimentation of starch-filled amyloplasts and relocalization of the auxin transport protein, PIN3. Gibberellic acid treatment stimulates the rate of tension wood formation and gravibending and enhances tissue-specific expression of an auxin-responsive reporter. Gravibending, maturation of contractile fibers, and gibberellic acid (GA) stimulation of tension wood formation are all sensitive to transcript levels of the Class I KNOX homeodomain transcription factor-encoding gene ARBORKNOX2 (ARK2). We generated genome-wide transcriptomes for trees in which gene expression was perturbed by gravistimulation, GA treatment, and modulation of ARK2 expression. These data were employed in computational analyses to model the transcriptional networks underlying wood formation, including identification and dissection of gene coexpression modules associated with wood phenotypes, GA response, and ARK2 binding to genes within modules. We propose a model for gravitropism in the woody stem in which the peripheral location of PIN3-expressing cells relative to the cambium results in auxin transport toward the cambium in the top of the stem, triggering tension wood formation, while transport away from the cambium in the bottom of the stem triggers opposite wood formation.
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CitationGerttula, Suzanne; Zinkgraf, Matthew; Muday, Gloria K.; Lewis, Daniel R.; Ibatullin, Farid M.; Brumer, Harry; Hart, Foster; Mansfield, Shawn D.; Filkov, Vladimir; Groover, Andrew. 2015. Transcriptional and Hormonal Regulation of Gravitropism of Woody Stems in Populus. The Plant Cell. 27(10): 2800-2813.
KeywordsCambium, tension wood, biofuels
- The Populus homeobox gene ARBORKNOX2 regulates cell differentiation during secondary growth
- The Populus Class III HD ZIP, popREVOLUTA, influences cambium initiation and patterning of woody stems
- Identifying gene coexpression networks underlying the dynamic regulation of wood-forming tissues in Populus under diverse environmental conditions
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