New Phytologist Review Tansley review Evolution of development of vascular cambia and secondary growth Author for correspondence: Rachel Spicer1 and Andrew Groover2 Andrew Groover 1The Rowland Institute at Harvard, Cambridge, MA, USA; 2Institute of Forest Genetics, Pacific Tel: +1 530 759 1738 Email:
[email protected] Southwest Research Station, USDA Forest Service, Davis, CA, USA Received: 29 December 2009 Accepted: 14 February 2010 Contents Summary 577 V. Evolution of development approaches for the study 587 of secondary vascular growth I. Introduction 577 VI. Conclusions 589 II. Generalized function of vascular cambia and their 578 developmental and evolutionary origins Acknowledgements 589 III. Variation in secondary vascular growth in angiosperms 581 References 589 IV. Genes and mechanisms regulating secondary vascular 584 growth and their evolutionary origins Summary New Phytologist (2010) 186: 577–592 Secondary growth from vascular cambia results in radial, woody growth of stems. doi: 10.1111/j.1469-8137.2010.03236.x The innovation of secondary vascular development during plant evolution allowed the production of novel plant forms ranging from massive forest trees to flexible, Key words: forest trees, genomics, Populus, woody lianas. We present examples of the extensive phylogenetic variation in sec- wood anatomy, wood formation. ondary vascular growth and discuss current knowledge of genes that regulate the development of vascular cambia and woody tissues. From these foundations, we propose strategies for genomics-based research in the evolution of development, which is a next logical step in the study of secondary growth. I. Introduction this pattern characterizes most extant forest trees, significant variation exists among taxa, ranging from extinct woody Secondary vascular growth provides a means of radially lycopods and horsetails with unifacial cambia (Cichan & thickening and strengthening plant axes initiated during Taylor, 1990; Willis & McElwain, 2002), to angiosperms primary, or apical growth.