First steps in studying the origins of secondary woodiness in Begonia (Begoniaceae): combining anatomy, phylogenetics, and stem transcriptomics

Since Darwin's observation that secondary woodiness is common on islands, the evolution of woody plants from herbaceous ancestors has been documented in numerous angiosperm groups. However, the evolutionary processes that give rise to this phenomenon are poorly understood. To begin addressing this we have used a range of approaches to study the anatomical and genetic changes associated with the evolution and development of secondary woodiness in a tractable group. Begonia is a large, mainly herbaceous, pantropical genus that shows multiple shifts towards secondarily woody species inhabiting mainly tropical montane areas throughout the world. Molecular phylogenies, including only a sample of the woody species in Begonia, indicated at least eight instances of a herbaceous-woody transition within the genus. Wood anatomical observations of the five woody species studied revealed protracted juvenilism that further support the secondary derived origin of wood within Begonia. To identify potential genes involved in shifts towards secondary woodiness, stem transcriptomes of wood development in B. burbidgei were analysed and compared with available transcriptome datasets for the non-woody B. venustra, B. conchifolia, and Arabidopsis, and with transcriptome datasets for wood development in Populus. Results identified a number of potential regulatory genes as well as variation in expression of key biosynthetic enzymes. (C) 2015 The Authors. Biological Journal of the Linnean Society published by John Wiley & Sons Ltd on behalf of Linnean Society of London,