Histone H3K4 methyltransferase ATX1 positively regulates secondary wall biosynthesis in interfascicular fibers in Arabidopsis

Secondary wall thickening in the sclerenchyma cells is strictly controlled by a complex network of transcription factors in vascular plant. However, little is known about the epigenetic mechanism regulating secondary cell wall biosynthesis. Genome-wide analysis revealed that the up-regulation of genes involved in secondary wall formation during stem development is largely coordinated by increasing level of H3K4 tri-methylation. In this study, we identified that ARABIDOPSIS HOMOLOG of TRITHORAX1 (ATX1), a H3K4-histone methyltransferase, positively regulates secondary wall deposition mainly through activating the expression of secondary wall NAC master switch genes, SECONDARY WALL-ASSOCIATED NAC DOMAIN PROTEIN1 (SND1) and NAC SECONDARY WALL THICKENING PROMOTING FACTOR1 (NST1). Overall design: Examination of the difference of transcriptiomes and H3K4me3 modifications in the stem of wild type (Col) and atx1 mutant grown to 20cm. The stem is divided into four stages from top to bottom. Stage I 0-3cm, stage II 5-7cm, stage III 10-12cm, stage IV 18-20cm