H2A.Z promotes the transcription of <i>MIR156A</i> and <i>MIR156C</i> in <i>Arabidopsis</i> by facilitating the deposition of H3K4me3

Abstract

Vegetative phase change in <i>Arabidopsis thaliana</i> is mediated by a decrease in the level of <i>MIR156A</i> and <i>MIR156C</i>, resulting in an increase in the expression of their targets, SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) genes. Changes in chromatin structure are required for the downregulation of <i>MIR156A</i> and <i>MIR156C</i>, but whether chromatin structure contributes to their initial elevated expression is unknown. We found that mutations in components of the SWR1 complex (<i>ARP6</i>, <i>SEF</i>) and in genes encoding H2A.Z (<i>HTA9</i> and <i>HTA11</i>) reduce the expression of <i>MIR156A</i> and <i>MIR156C</i>, and accelerate vegetative phase change, indicating that H2A.Z promotes juvenile vegetative identity. However, <i>arp6</i> and <i>sef</i> did not accelerate the temporal decline in miR156, and the downregulation of <i>MIR156A</i> and <i>MIR156C</i> was not accompanied by significant change in the level of H2A.Z at these loci. We conclude that H2A.Z contributes to the high expression of <i>MIR156A/MIR156C</i> early in shoot development, but does not regulate the timing of vegetative phase change. Our results also suggest that H2A.Z promotes the expression of <i>MIR156A/MIR156C</i> by facilitating the deposition of H3K4me3, rather than by decreasing nucleosome occupancy.