Role of cellulose synthase-like (csl) genes in barley root growth and differentiation

Lou, Haoyu (2020) Role of cellulose synthase-like (csl) genes in barley root growth and differentiation. PhD thesis, University of Nottingham.

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Abstract

Barley is a commercial important crop with multiple utilisations. It is widely used in the malting and brewing industries, and with rising attention as super food for its high dietary fibre content. Intensive studies have focused on grain development to improve grain quality to benefit agricultural practices. Less attention has been given to root development. Roots are important plant organs that provide mechanical strength to anchor plants to soil substrates. Roots are also responsible for water and nutrients capture and transportation to aerial organs to support plant development. From the root apical meristem, cells undergo rapid division to form different tissues in the meristem zone, followed by longitudinal expansion to enlarge cell size in the elongation zone, and complete final differentiation in the maturation zone to form fully functional root cells. During this process, cell wall biosynthesis and assembly are critical determinants because the rapidly enlarging cells require strength to resist internal pressure, and also flexibility to allow unidirectional cell expansion. Plant cell walls are composed of various polymers, including cellulose, hemicelluloses, and pectins, which confer distinct chemical and mechanical properties. Cell wall polysaccharide heterogeneity has been described in various tissues and species including Arabidopsis roots and barley developing grains. However, very limited knowledge on the relationships between the composition of root tip cell walls and the development of barley roots has been reported due to the complexity and heterogeneity of the roots. The work presented in this thesis aimed to identify the roles of two cell wall related genes belonging to the Cellulose Synthase-Like (Csl) family during root tip development.

To gain a better understanding of gene regulation and polysaccharide composition in the barley root tip, we first analysed the expression of the Csl genes in different root regions and showed predominate expression of HvCslF3 and HvCslF9 genes in the meristem and elongation zones. Cell wall polysaccharide composition of barley root tips was determined by immunohistochemistry and glycosidic linkage analysis.

To further understand the functions of the HvCslF3 and HvCslF9 genes in the barley root tip, we employed RNAi to generate knock-down mutants, and analysed the morphological and dynamic differences between the mutants and the wild-type cultivar Golden Promise. These genes are essential in maintaining seminal root elongation and cortical radial patterning of seedlings. The potential functions of HvCslF3 and HvCslF9 genes in regulating the synthesis of cell wall polysaccharides, (1,4)-β-linked glucoxylan and (1,3;1,4)-β-glucan, respectively, were revealed. This indicates that cell wall composition affects root development as a smaller root system was observed in the mutant barley seedlings.

Notably, the restrictions on root development were not limited to seedlings. Indeed, we also show the reduction in the root systems and aerial tissue development in the glasshouse grown mutant plants throughout the vegetative growth. The smaller root systems resulted in limitation on water and nutrient uptake. Transportation may be the main reason behind the decreased development of aerial organs. To support this hypothesis, mathematical modelling was used to predict the difference in water and nutrients capture between the genotypes. The simulations also highlighted the variations on plant performance in response to nutrient stresses. Interestingly, the mutant root systems contain certain traits that are beneficial for the plant to tolerate low nutrient availabilities. These findings suggested a new direction in plant breeding to generate plants with more efficient root traits based on cell wall related gene expression and regulation.

A phylogenetic study indicated the close relationship between the CslF and CslD gene families. The Arabidopsis genome lacks CslF genes and the plant therefore provides an excellent heterologous expression system to study the functions of HvCslF genes. By introducing the HvCslF3 gene into wild-type Arabidopsis (Col-0) plants and root hair mutants deficient in AtCslD3 and AtCslD5, we demonstrated the functional redundancy between the CslD and CslF gene families and identified a role for HvCslF3 in root hair cell file specification and root hair elongation.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Bulone, Vincent
Tucker, Matthew
Bennett, Malcolm
Band, Leah
Keywords: Cell wall, Barley, Root development, Cellulose synthase-like, Differentiation
Subjects: S Agriculture > SB Plant culture
Faculties/Schools: UK Campuses > Faculty of Science > School of Biosciences
Item ID: 61238
Depositing User: Lou, Haoyu
Date Deposited: 08 Sep 2020 08:24
Last Modified: 08 Sep 2020 08:30
URI: http://eprints.nottingham.ac.uk/id/eprint/61238

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