Genome-wide determination of Puccinia psidii s.l. rust resistance in eucalypts (ARC-Linkage Project LP130100458)

Gerd Bossinger, Peter K Ades, Antanas V Spokevicius, Josquin FG Tibbits (DEDJTR – AgriBio), Wilson TL Yong, Fatima A Runa, Paul WJ Taylor (FVAS), Richard Kerr (STBA), Philippe Rigault (Gydle Inc), Karanjeet Sandhu (USyd), Brad M Potts (UTas)

This project represents a major collaborative effort led by UM’s FMBG team with support and significant intellectual input from the Southern Tree Breeding Association (STBA); Hancock Victorian Plantations (HVP); VicForests; Australian Bluegum Plantations Pty Ltd (ABP); the Victorian Government Department of Economic Development Jobs Transport and Resources (DEDJTR) through AgriBio; the NSW Government Department of Trade & Investment Regional Infrastructure and Services (DTIRIS) through its Biosecurity Research Division; Gydle Inc (Canada); the University of Sydney and the University of Tasmania.

Native to South-eastern Australia, Eucalyptus globulus is the main eucalypt grown in pulpwood plantations in temperate regions worldwide. In this project, large progeny screenings of E. globulus have been conducted for myrtle rust (Austropuccinia psidii) resistance including germplasm from wild trees across the native range and selections from breeding programs. In total some 14,000 E. globulus plants (from over 2,000 seedlots) were screened, in addition to some 2,000 plants (from over 900 native seedlots) of E. obliqua, another economically important eucalypt species. To our knowledge, this represents the largest screening for myrtle rust in any plant species to date. The screened material was used (i) to study the infection process and disease cycle of Austropuccinia psidii, (ii) to uncover geographical patterns of variation in susceptibility of E. globulus and E. obliqua to myrtle rust disease; and (iii) to conduct genome wide association studies of myrtle rust resistance in E. obliqua and E. globulus, the latter with special focus on the Australian deployment and breeding collections (see below).


Phenotypic variation of myrtle rust resistance in Eucalyptus globulus (sub-project of LP130100458)

Fatima A Runa, Gerd Bossinger, Peter K Ades, Josquin FG Tibbits (DEDJTR – AgriBio), Wilson TL Yong, Karanjeet S Sandhu (USyd)

Myrtle rust disease, caused by the fungal pathogen Austropuccinia psidii s.l. has a wide host range within Myrtaceae and poses a significant threat to Myrtaceae-rich ecosystems and Myrtaceae-based industries around the world. In this project, we provide a detailed characterisation of E. globulus resistance to A. psidii and estimate genetic parameters based on the largest progeny screening for myrtle rust resistance in any plant species to date. In total we screened 6935 E. globulus plants from 444 seedlots representing an almost complete survey of the Australian deployment and breeding collections. We investigate possible genetic mechanisms for resistance and explore options for the incorporation of myrtle rust resistance traits into current breeding programs.


Identification of transcriptome changes in response to water deficit in different species of Eucalyptus with contrasting drought sensitivity

Mojtaba K Raad, Andrew Merchant (USyd), Josquin FG Tibbits (DEDJTR – AgriBio), Gerd Bossinger, Antanas V Spokevicius

Changes in global climate have been a major driver for evolution. In plants, stresses related to lack or excess of water, light and heat, combined or in isolation, required individuals and populations to develop different physiological, morphological and molecular mechanisms to survive and flourish. Australian plants like eucalypts have evolved in response to climate change during different geographical periods and increasing length and intensity of drought in different parts of Australia led to a series of adaptations. Aiming to better understand adaptation mechanisms, this project analyses changes in gene expression patterns and metabolite profiles in a diverse range of eucalypt species from different geographic locations, from mesic and xeric backgrounds, in response to different water stress conditions. Our results are hoped to inform sustainable forest management and support breeding efforts and deployment practices.


Functional investigations into transcription factors behind wood formation

Nadeeshani Karannagoda, Steven Hussey (University of Pretoria), Antanas Spokevicius, Gerd Bossinger

Xylogenesis is a continuous and dynamic differentiation process of cambial cell division, differentiation, xylem cell expansion, secondary cell wall (SCW) deposition and programmed cell death. All these stages are transcriptionally regulated by an underlying network of transcription factors (TFs). This project uses transgenic Eucalyptus grandis x camaldulensis hybrid and Populus alba somatic xylem tissue sectors to functionally characterise a number of selected Eucalyptus grandis transcription factors that have not previously been investigated for their role in wood formation. Observed changes in wood cell morphology and biochemistry will shed light on the transcriptional network regulating SCW deposition in economically and ecologically important woody tree species.


Tubulin roles in determining cellulose microfibril angle during wood formation

Larissa Machado Tobias, Heather McFarlane (University of Toronto), Antanas Spokevicius, Gerd Bossinger

In commercially grown woody tree species, the orientation of cellulose microfibrils within the secondary cell wall (microfibril angle – MFA) is an important wood quality determinant and a major domestication trait. MFA varies along the plant’s developmental gradients and in reaction wood is formed in response to gravitational stress. Tubulin genes, encoding the primary components of microtubules, are known to be differentially expressed in reaction wood and to affect the MFA of xylem fibres. This project investigates how tubulin proteins participate in MFA determination by providing a visual assessment of microtubule organisation and orientation in fixed cells of xylem excised from reaction, opposite and normal wood from branches and induced systems in eucalypt, poplar and radiata pine. Results are expected to shed light on the role played by tubulin genes in orientating cellulose microfibrils during the deposition of secondary cell walls in woody trees.


Unveiling the molecular control of bifacial cambium development in trees

Sachinthani Karunarathne, Antanas Spokevicius, John Golz (BioSciences), Gerd Bossinger

In contrast to animals with predetermined growth patterns, plant growth is continuous and iterative producing new organs and structures from actively dividing meristems. In woody tree species, one such meristem is the bifacial vascular cambium which continuously produces phloem or bark towards the outside of the trunk and xylem or wood towards the inside. How is this continuity re-established after the cambium itself has been wounded or partially destroyed? What are the mechanisms that enable trees to maintain or re-establish secondary vascular tissue (SVT)? In this project we use wound response as a tool to investigate molecular level controls of cambium re-establishment and regeneration of SVT patterns. Genes and hormones known to interact in the differentiation of xylem, phloem and cambium domains in different woody tree species are being assessed for their respective roles in cambium regeneration upon wounding. Results will provide insights into the molecular control of radial pattern formation in newly establishing cambia adding to our rapidly expanding knowledge about vascular proliferation processes also in established cambia.