Specific Eucalyptus grandis Tubulin Isoforms Are Involved in Determining the Orientation of Cellulose Microfibrils in the Secondary Cell Wall of Wood Fibres

Cortical microtubules comprise heterodimeric units of α- and β-tubulin which have been shown to guide the deposition of cellulose microfibrils in plant cell walls where their arrangement is important in determining cell morphology and cell wall properties. Tubulin genes are highly expressed in woody tissues and a functional study has demonstrated a role for a β-tubulin gene family member in affecting the orientation of cellulose microfibrils in wood fibre cells, an important trait in determining the mechanical properties of wood fibres. To further understand the role of tubulins in plant cell trait determination, this study identified and investigated the expression of the α- and β-tubulin gene families in Eucalyptus and then, using transgenesis techniques, investigated the role of specific eucalypt tubulin isoforms in determining secondary cell wall traits of wood fibres in plant stems. This study found that the α- and β-tubulin gene families in Eucalyptus are relatively small compared to other species and show higher expression in woody stem tissue when compared to leaf. Functional studies revealed that cambial cells transformed with α- and β-tubulin overexpression and knockdown vectors, either on their own or in combination, lead to changes in the angle of microfibrils in the secondary cell wall of wood fibre cells with Class I- and Class I-like gene family members explicitly involved. This study demonstrates the importance of tubulins in determining the mechanical properties of wood fibres through a mechanism involving specific tubulin isoform expression during wood fibre formation.