KNAT2/6b, a class I KNOX gene, impedes xylem differentiation by regulating NAC domain transcription factors in poplar

• Published in: The New phytologist 2020-02, Vol.225 (4), p.1531-1544
• Main Authors: Zhao, Yanqiu, Song, Xueqin, Zhou, Houjun, Wei, Kaili, Jiang, Cheng, Wang, Jinnan, Cao, Yuan, Tang, Fang, Zhao, Shutang, Lu, Meng-Zhu
• Format: Article
• Language: English
• Subjects: Cell differentiation; Cell Wall - chemistry; Cell walls; Cellulose; Differentiation (biology); Domains; Gene Expression Regulation, Plant - physiology; Gene sequencing; Genes; Hardwoods; KNOX gene; Lignin; NAC domain; Nucleic acids; PagKNAT2/6b; Plant Proteins - genetics; Plant Proteins - metabolism; Poplar; Populus; Populus - genetics; Populus - growth & development; Populus - metabolism; Regulators; Ribonucleic acid; RNA; RNA sequencing; RNA, Plant - genetics; RNA, Plant - metabolism; secondary wall; Transcription; Transcription activation; Transcription factors; Transcription Factors - genetics; Transcription Factors - metabolism; Transgenic plants; Wall deposition; Wood; Wood - growth & development; XND1; Xylem; xylem differentiation
• ISSN: 0028-646X; 1469-8137
• DOI: 10.1111/nph.16036

• Wood formation is the terminal differentiation of xylem mother cells derived from cambial initials, and negative regulators play important roles in xylem differentiation. • The molecular mechanism of the negative regulator of xylem differentiation PagKNAT2/6b was investigated. PagKNAT2/6b is an ortholog of Arabidopsis KNAT2 and KNAT6 that is highly expressed in phloem and xylem. Compared to nontransgenic control plants, transgenic poplar plants overexpressing PagKNAT2/6b present with altered vascular patterns, characterized by decreased secondary xylem with thin cell walls containing less cellulose, xylose and lignin. • RNA sequencing analyses revealed that differentially expressed genes are enriched in xylem differentiation and secondary wall synthesis functions. Expression of NAM/ATAF/CUC (NAC) domain genes including PagSND1-A1, PagSND1-A2, PagSND1-B2 and PagVND6-C1 is downregulated by PagKNAT2/6b, while PagXND1a is directly upregulated. Accordingly, the dominant repression form of PagKNAT2/6b leads to increased xylem width per stem diameter through downregulation of PagXND1a. • PagKNAT2/6b can inhibit cell differentiation and secondary wall deposition during wood formation in poplar by modulating the expression of NAC domain transcription factors. Direct activation of PagXND1a by PagKNAT2/6b is a key node in the negative regulatory network of xylem differentiation by KNOXs.