Wood fibres are a vital structural component of tree strength and flexibility. However, relatively little is known about the genetic control of fibre strength. The structural properties of wood fibres are largely determined by the strength and flexibility of their cell walls, which are produced during secondary growth. Cellulose microfibril deposition during primary growth is known to be guided by cortical microtubules. Microtubules are formed from heterodimers of alpha and beta-tubulins, and also have other roles in intracellular transport, cell division and morphology. Here we report on how we have investigated the molecular control of microtubule formation and its linked control of cellulose microfibril deposition during secondary growth in eucalypts. We have used an in vivo transformation system (Induced Somatic Sector Analysis; ISSA) to modify the expression of alpha and beta-tubulin genes in developing wood, resulting in the formation of small transgenic wood sectors within stems of established trees. Significant phenotypic changes (-2 to 4 degrees) in the orientation of cellulose microfibrils were observed in transgenic wood fibre cell walls when compared to directly neighbouring control tissue.
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