Analysis of Orthologous SECONDARY WALL-ASSOCIATED NAC DOMAIN1 (SND1) Promotor Activity in Herbaceous and Woody Angiosperms.

Libert B Tonfack,Steven G Hussey,Eshchar Mizrachi,Adri Veale,Alexander A Myburg

doi:10.3390/ijms20184623

Libert B Tonfack, Steven G Hussey + Show 3 more

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https://doi.org/10.3390/ijms20184623

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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. β-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.

Highlights

The bioengineering of secondary cell walls (SCWs) in woody plants is a highly active area of research that relies on a thorough understanding of the complexity of SCW transcriptional regulation
We have a poor understanding of the transcription factors and associated cis-regulatory elements that regulate the secondary wall-associated NAC domain protein 1 (SND1) promoter; among the few reported interactions in Arabidopsis are those of LBD30 [16], transcriptional repressors MYB4, MYB7 and MYB32 [17] as well as SND1 itself [17]
We obtained a similar tree topology between Arabidopsis and Populus WND1 proteins according to previous reports [19,32], and a topology congruent with that of our previous family-wide NAC protein analysis [26], which included the Eucalyptus secondary wall NACs (SWNs) proteins (Figure 1a)

Summary

Introduction

The bioengineering of secondary cell walls (SCWs) in woody plants is a highly active area of research that relies on a thorough understanding of the complexity of SCW transcriptional regulation. Secondary wall-associated NAC domain protein 1 (SND1), known as NAC secondary wall thickening promoting factor 3 (NST3) or ANAC012, yielded a predominantly interfascicular and xylary fibre-specific SCW reduction phenotype following dual knock-out of SND1 and its functionally redundant homolog NST1 [10,11]. This led to an interpretation of a fibre-specific role for SND1 in SCW regulation, silique valve and endothecium SCWs were reportedly affected [12,13]. We have a poor understanding of the transcription factors and associated cis-regulatory elements that regulate the SND1 promoter; among the few reported interactions in Arabidopsis are those of LBD30 [16], transcriptional repressors MYB4, MYB7 and MYB32 [17] as well as SND1 itself [17]

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