Light Quality-Mediated Petiole Elongation in Arabidopsis during Shade Avoidance Involves Cell Wall Modification by Xyloglucan Endotransglucosylase/Hydrolases

Rashmi Sasidharan, C. C. Chinnappa, Marten Staal, J. Theo M. Elzenga, Ryusuke Yokoyama, Kazuhiko Nishitani, Laurentius A. C. J. Voesenek, Ronald Pierik*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

138 Citations (Scopus)
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Abstract

Some plants can avoid shaded conditions via rapid shoot elongation, thus growing into better lit areas in a canopy. Cell wall-modifying mechanisms promoting this elongation response, therefore, are important regulatory points during shade avoidance. Two major cell wall-modifying protein families are expansins and xyloglucan endotransglucosylase/hydrolases (XTHs). The role of these proteins during shade avoidance was studied in Arabidopsis (Arabidopsis thaliana). In response to two shade cues, low red to far-red light (implying neighbor proximity) and green shade (mimicking dense canopy conditions), Arabidopsis showed classic shade avoidance features: petiole elongation and leaf hyponasty. Measurement of the apoplastic proton flux in green shade-treated petioles revealed a rapid efflux of protons into the apoplast within minutes, unlike white light controls. This apoplastic acidification probably provides the acidic pH required for the optimal activity of cell wall-modifying proteins like expansins and XTHs. Acid-induced extension, expansin susceptibility, and extractable expansin activity were similar in petioles from white light-and shade-treated plants. XTH activity, however, was high in petioles exposed to shade treatments. Five XTH genes (XTH9, -15, -16, -17, and -19) were positively regulated by low red to far-red light conditions, while the latter four and XTH22 showed a significant up-regulation also in response to green shade. Consistently, knockout mutants for two of these XTH genes also had reduced or absent shade avoidance responses to these light signals. These results point toward the cell wall as a vital regulatory point during shade avoidance.

Original languageEnglish
Pages (from-to)978-990
Number of pages13
JournalPlant Physiology
Volume154
Issue number2
DOIs
Publication statusPublished - Oct-2010

Keywords

  • EXPANSIN GENE-EXPRESSION
  • DIFFERENTIAL EXPRESSION
  • RUMEX-PALUSTRIS
  • PRIMARY ROOT
  • XTH FAMILY
  • GROWTH
  • THALIANA
  • PLANTS
  • EXTENSION
  • ENZYMES

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