BETWOOD · Identification of novel regulators of growth and wood formation by studying natural variation in Arabidopsis and Betula pendula, a novel model tree

Periodic Report Summary 1 - BETWOOD (Identification of novel regulators of growth and wood formation by studying natural variation in Arabidopsis and Betula pendula, a novel model tree)

Wood, the secondary xylem of plants, is produced through the activity of vascular cambium. Wood both enables water transport to the shoot and provides structural support for it by its thick secondary cell walls. Our research aims to understand the molecular mechanisms controlling wood formation in plants. We are working to identify novel genes functioning in regulation of cambial meristem activity by exploring the natural variation present in this process. We are interested in factors regulating both the rate of cambial cell divisions (the rate of wood production) (Immanen et al. 2013, Sankar et al. 2014, Randall et al. 2015, Immanen et al. in press) and the characteristics of differentiating xylem cells (the quality of produced wood). The quality of wood is determined by the identity (fibers vs vessels), morphology (width vs height, cell wall thickness) and secondary cell wall composition of xylem cells. Through the regulation of biomass allocation, wood formation traits are affected by the genetic regulation of plant architecture (Chevalier et al. 2014). Our research has immense potential for the forest industry: the identified molecular regulators represent optimal target genes for tree breeding and forest biotechnology. We are exploring two complementary model species: herbaceous Arabidopsis thaliana and forest trees. Despite its small size, Arabidopsis produces wood and has emerged as a versatile model for plant vascular development (Zhang et al. 2014, Allahverdiyeva et al. 2015, and Nieminen et al. 2015). The main focus of my research is on silver birch, an important forestry tree with multiple favourable traits which make it an ideal genetic model tree. Silver birch is one of the most important boreal hardwood forestry trees: it is currently used mainly for pulp, paper, cardboard, plywood and sawn goods. Silver birch has several specific features which give it an advantage in genetic research: 1) possibility for inbreeding (and respectively increased homozygosity), 2) radically shortened generation time through artificially induced flowering, and 3) an available collection of naturally occurring atypical birch wood formation and morphology mutants. With birch as the model tree, our project represents a novel approach of tree genetics, which has potential for ground-breaking insights into wood development. The researcher, Dr. Kaisa Nieminen, has a Research Scientist position at the Natural Resources Institute Finland (Luke): the project brings together the basic research conducted in close collaboration with the University of Helsinki and the ongoing tree breeding program at the Natural Resources Institute Finland (Luke). References Allahverdiyeva Y, Battchikova N, Brosché M, Fujii H, Kangasjärvi S, Mulo P, Mähönen AP, Nieminen K, Overmyer K, Salojärvi J, Wrzaczek M. 2015. Integration of photosynthesis, development and stress as an opportunity for plant biology. New Phytol. doi: 10.1111/nph.13549. Review. Chevalier F, Nieminen K, Sánchez-Ferrero JC, Rodríguez ML, Chagoyen M, Hardtke CS, Cubas P. 2014. Strigolactone Promotes Degradation of DWARF14, an alpha/beta Hydrolase Essential for Strigolactone Signaling in Arabidopsis. Plant Cell. 26:1134-1150. Immanen J, Nieminen K, Duchens Silva H, Rodríguez Rojas F, Meisel LA, Silva H, Albert VA, Hvidsten TR, Helariutta Y. 2013. Characterization of cytokinin signaling and homeostasis gene families in two hardwood tree species: Populus trichocarpa and Prunus persica. BMC Genomics. 14:885. Immanen J, Nieminen K, Smolander OP, Kojima M, Alonso Serra J, Koskinen P, Zhang J, Elo A, Mähönen AP, Street N, Bhalerao RP, Paulin L, Auvinen P, Sakakibara H, Helariutta Y. Cytokinin and auxin display distinct but interconnected distribution and signaling profiles to stimulate cambial activity. Current Biology, in press. Nieminen K, Blomster T, Helariutta Y, Mähönen AP. 2015. Vascular Cambium Development. In The Arabidopsis Book 13: e0177. doi: http://dx.doi.org/10.1199/tab.0177. Online book chapter. Randall RS, Miyashima S, Blomster T, Zhang J, Elo A, Karlberg A, Immanen J, Nieminen K, Lee JY, Kakimoto T, Blajecka K, Melnyk CW, Alcasabas A, Forzani C, Matsumoto-Kitano M, Mähönen AP, Bhalerao R, Dewitte W, Helariutta Y, Murray JA. 2015. AINTEGUMENTA and the D-type cyclin CYCD3;1 regulate root secondary growth and respond to cytokinins. Biol Open. doi: 10.1242/bio.013128. Sankar M, Nieminen K, Ragni L, Xenarios I, Hardtke CS. 2014. Automated quantitative histology reveals vascular morphodynamics during Arabidopsis hypocotyl secondary growth. Elife. 3:e01567. Zhang J, Nieminen K, Serra JA, Helariutta Y. 2014. The formation of wood and its control. Curr Opin Plant Biol. 17:56-63. Review.

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