Arabidopsis JMJ29 is involved in trichome development by regulating the core trichome initiation gene GLABRA3

Plant trichomes are large single cells that are organized in a regular pattern and play multiple biological functions. In Arabidopsis, trichome development is mainly governed by the core trichome initiation regulators, including the R2R3 type MYB transcript factor GLABRA 1 (GL1), bHLH transcript factors GLABRA 3/ENHANCER OF GLABRA 3 (GL3/EGL3), and the WD-40 repeat protein TRANSPARENT TESTA GLABRA 1 (TTG1), as well as the downstream trichome regulator GLABRA 2 (GL2). GL1, GL3/EGL3, and TTG1 can form a trimeric activation complex to activate GL2, which is required for the trichome initiation and maintenance during cell differentiation. Arabidopsis JMJ29 is a JmjC domain-containing histone demethylase belonging to the JHDM2/KDM3 group. Members of the JHDM2/KDM3 group histone demethylases are mainly responsible for the H3K9me1/2 demethylation. In the present study, we found that the trichome density on leaves and inflorescence stems is significantly decreased in jmj29 mutants. The expression of the core trichome regulators GL1, GL2, and GL3 is decreased in jmj29 mutants as well. Furthermore, JMJ29 can directly target GL3 and remove H3K9me2 on the GL3 locus. Collectively, we found that Arabidopsis JMJ29 is involved in trichome development by directly regulating GL3 expression. These results provide further insights into the molecular mechanism of epigenetic regulation in Arabidopsis trichome development.