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Doctoral thesis, 2018

Elucidating the phytohormonal control of xylem development

Johnsson, Christoffer


Secondary xylem, commonly known as wood, has had a major impact on both our planet and civilization, its uses so ubiquitous that it is often taken for granted in daily life. New challenges imposed by growing population and changing climate have led academia and industries to search for ways of altering wood characteristics to better suit specific purposes. Achieving this by genetic engineering requires the ability to alter gene expression in specific cell types, while avoiding alterations in others. This calls for an in depth understanding of the factors directing the differentiation and development of the cell types constituting secondary xylem. Studies detailed in this thesis exhibit my attempts to link the signals of the phytohormones auxin and gibberellic acid to the formation of fibres, and their deposition of thick secondary cell walls. Using high resolution RNA-sequencing data gathered across developing Populus wood, I was able to illustrate that the expression profiles of various wood-associated transcription factors are distinct, in relation to their functions. Furthermore, I investigated the response of gene expression and tissue anatomy to treatment by auxin and gibberellin and found that auxin down-regulates transcription factors previously identified as master regulators of fibre secondary cell wall formation, as well as impede secondary wall development on a tissue level. At the same time, gibberellic acid appears to have a general enhancing effect on the expression of the same genes, and is better able to rescue the tissue phenotype of decapitated Populus plants. I also highlight a role for gibberellic acid in the differentiation of fibre cells through DELLA regulated interaction of Class I KNOX transcription factors with proteins of the NUCLEAR FACTOR Y family. These findings suggest that an integration of auxin and gibberellin signals, acting through multiple pathways, is responsible for the correct spatiotemporal differentiation and development of the secondary xylem.


Xylem, Auxin, Gibberellin, differentiation, secondary cell wall

Published in

Acta Universitatis Agriculturae Sueciae
2018, number: 2018:20
ISBN: 978-91-7760-180-7, eISBN: 978-91-7760-181-4
Publisher: Department of Forest Genetics and Plant Physiology

Authors' information

Johnsson, Christoffer (Johnsson, Christoffer)
Swedish University of Agricultural Sciences, Department of Forest Genetics and Plant Physiology

UKÄ Subject classification

Developmental Biology
Other Industrial Biotechnology

URI (permanent link to this page)