Strigolactones inhibit adventitious root formation

Amanda Rasmussen (2010). Strigolactones inhibit adventitious root formation PhD Thesis, School of Biological Sciences, The University of Queensland.

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s40267612_100wordabstract.pdf abstract (short version) application/pdf 4.81KB 4
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Author Amanda Rasmussen
Thesis Title Strigolactones inhibit adventitious root formation
School, Centre or Institute School of Biological Sciences
Institution The University of Queensland
Publication date 2010-11
Thesis type PhD Thesis
Supervisor Assoc. Prof. Christine Beveridge
Prof. Christa Critchley
Total pages 142
Total colour pages 10
Total black and white pages 132
Subjects 06 Biological Sciences
Abstract/Summary Adventitious root formation from a non-root tissue facilitates clonal propagation of elite plant varieties and is therefore central to many plant industries worldwide. However many plant species cannot be propagated in this way posing significant limitations particularly on the forestry and horticulture industries. Although clonal propagation has been used for centuries, we have only recently begun to understand the process of adventitious root formation at the genetic, molecular and biochemical levels. Adventitious root initiation is regulated by many hormones including auxin and cytokinins. The research described in this thesis discovered a new function for strigolactones as a regulator of adventitious rooting. Strigolactones, known for their role in shoot branching, were clearly involved in the suppression of adventitious root initiation in two biological systems: pea stem cuttings and Arabidopsis seedling hypocotyls. The CYCB1:GUS marker together with microscopy of strigolactone mutants in both systems, established that strigolactones limit the size of the region in which adventitious roots can initiate (rooting zone). There was no difference in the density of adventitious roots within the rooting zone and there was no evidence of unfinished primordia within wild type and strigolactone mutant plants. To determine if strigolactones may play a wider role in plant development, pea and Arabidopsis strigolactone mutants were also screened for developmental phenotypes such as germination, intact primary root growth and lateral root branching, but only primary root growth was affected and the phenotype was quite subtle. In order to understand how strigolactones function in concert with other hormones already known to be involved in adventitious rooting, the interactions of strigolactones with cytokinins and auxins were investigated. Arabidopsis cytokinin production and response mutants (ipt1 ipt5 ipt7 triple mutant and ahk3 ahk4 double mutant, respectively) responded to strigolactones and the strigolactone deficient mutants responded to cytokinin. These findings were supported by grafting studies between wild type and strigolactone response mutants in pea and suggest that cytokinins and strigolactones likely act independently. Because auxin is important in adventitious root formation, the interaction between strigolactone and auxin was investigated using the Arabidopsis 35S:YUCCA1 auxin overproducing mutant and also using treatments with different types of auxin. Fewer adventitious roots were formed in 35S:YUCCA1 after strigolactone treatments compared to the control treatments and the strigolactone mutants of both pea and Arabdidopsis generated more adventitious roots in response to auxin treatments. This suggests that strigolactone does not act upstream of auxin biosynthesis and that auxin does not act directly upstream of strigolactone biosynthesis. It is possible though that strigolactone inhibits auxin transport, at least locally, and thereby reduces the amount of auxin that can build up in the rooting zone. Future research prompted by the data presented in this thesis should investigate a role for strigolactones in regulating auxin transport or also regulation of local auxin levels via conversion of IBA to IAA. Experimental reduction of strigolactone production in pea and Arabidopsis increased the number of adventitious roots that formed. Five ornamental species were also tested and adventitious rooting was improved by reduction of strigolactones in the species that were more difficult to root. These results suggest that manipulation of strigolactones could be used to improve adventitious rooting of commercially important and difficult-to-root species. Further research should test these theories and eventually this knowledge can be used to improve the cutting propagation of commercially important species.
Keyword Strigolactone
Cutting Propagation
Adventitious roots
primary root growth
Lateral Roots
Additional Notes In the PDF numbering: pages 35,45,46,58,60,66,67,72,74,76 are in colour

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Created: Fri, 29 Apr 2011, 02:07:58 EST by Miss Amanda Rasmussen on behalf of Library - Information Access Service