HAIRY MERISTEM proteins regulate the WUSCHEL protein levels in mediating CLAVATA3 expression.

The precise regulation of stem cells in the shoot apical meristems (SAMs) involves the function of the homeodomain transcription factor (TF)-WUSCHEL (WUS). WUS has been shown to move from the site of production-the rib-meristem (RM), into overlaying cells of the central zone (CZ), where it specifies stem cells and also regulates the transcription of CLAVATA3 (CLV3). The secreted signalling peptide CLV3 activates a receptor kinase signalling that restricts WUS transcription and also regulates the nuclear gradient of WUS by offsetting nuclear export. WUS has been shown to regulate both CLV3 levels and spatial activation, restricting its expression to a few cells in the CZ. The HAIRY MERISTEM (HAM), a GRASS-domain class of TFs expressed in the RM, has been shown to physically interact with WUS and regulate CLV3 expression. However, the mechanisms by which this interaction regulates CLV3 expression non-cell autonomously remain unclear. Here, we show that HAM function is required for regulating the WUS protein stability, and the CLV3 expression responds to altered WUS protein levels in ham mutants. Thus, HAM proteins non-cell autonomously regulates CLV3 expression.