**Acknowledgements**

Financial support from the Basque Government ELKARTEK KK-2016/00030 and KK-2017/00089 is greatly acknowledged. Miren Aguirre thanks the financial support given by the European Union (Woodlife project FP7-NMP-2009-SMALL-246434), the UPV/EHU (2984/2014) "Doktore berriak kontratatzeko eta horiek doktorego ondoko prestakuntza programetan sartzeko laguntza" and also the financial support received from Ministerio de Economía y Competitividad de España, Juan de la Cierva en Formación (FJCI-2014-22336). The SGIker UPV/EHU for the electron microscopy facilities of the Gipuzkoa unit is acknowledged. Programa de Grupos Consolidados from the Basque Government (IT999-16) is also gratefully acknowledged.
