Abstract:
SECONDARY WALL-ASSOCIATED NAC DOMAIN1 (SND1) is a master regulator of fibre
secondary wall deposition in Arabidopsis thaliana (Arabidopsis), with homologs in other angiosperms
and gymnosperms. However, it is poorly understood to what extent the fibre-specific regulation of
the SND1 promoter, and that of its orthologs, is conserved between diverged herbaceous and woody
lineages. We performed a reciprocal reporter gene analysis of orthologous SND1 promoters from
Arabidopsis (AthSND1), Eucalyptus grandis (EgrNAC61) and Populus alba P. grandidentata (PagWND1A)
relative to secondary cell wall-specific Cellulose Synthase4 (CesA4) and CesA7 promoters, in both a
non-woody (Arabidopsis) and a woody (poplar) system. -glucuronidase (GUS) reporter analysis in
Arabidopsis showed that the SND1 promoter was active in vascular tissues as previously reported
and showed interfascicular and xylary fibre-specific expression in inflorescence stems, while reporter
constructs of the woody plant-derived promoters were partial to the (pro)cambium-phloem and
protoxylem. In transgenic P. tremula P. alba plants, all three orthologous SND1 promoters expressed
the GUS reporter similarly and preferentially in developing secondary xylem, ray parenchyma and
cork cambium. Ours is the first study to reciprocally test orthologous SND1 promoter specificity in
herbaceous and woody species, revealing diverged regulatory functions in the herbaceous system.
