Genome-Wide Investigation of Knotted Related Homeobox Genes and Identification of a Fiber-Growth-Repressed Knotted Related Homeobox Gene in Ramie

The KNOX transcription factor plays crucial roles in regulating fiber growth in plants. Although the genome of ramie, an important fiber crop in China, is available, knotted related homeobox (KNOX) genes have not been systematically explored in this crop. In this study, seven members of the KNOX gene from the ramie genome were identified and assigned to two groups, Class I and II. The intron–exon structure, conserved domain architecture, cis-regulating elements, and expression pattern showed distinct differences among the seven KNOX regulators. One of the genes, Bnt07G011994, encodes an ortholog of Arabidopsis fiber-growth-related KNAT7, and is differentially expressed among barks undergoing different stages of fiber growth. The overexpression of Bnt07G011994 dramatically decreases the fiber number in transgenic Arabidopsis, indicating a negative role played by this gene in modulating fiber growth. Further transcriptome analysis of transgenic Arabidopsis revealed that the overexpression of Bnt07G011994 resulted in an expression change in 14 pectin biosynthesis-/metabolism-related genes. These findings provide a useful foundation for further investigating the function of KNOX genes in ramie, and provide an important insight into the involvement of the ramie KNOX gene in fiber growth.