Mutation of AtMMS21 caused misexpression of stem cell niche-defining transcription factors. The expression pattern of stem cell marker genes is shown in the roots of the wild type (WT) and mms21-1 at 5 DAG. A and B, pSHR:GFP. C and D, pSHR:SHR:GFP. E to G, pSCR:GFP. H to J, PLT1pro:PLT1:YFP. K to M, PLT2pro:PLT2:YFP. The insets in A to D show the expression of SHR, observed in the GFP channel. The arrowhead in D indicates that SHR localization was missing in some cell files in the mms21-1 roots. The arrowhead and arrows in F and G indicate discontinuous expression and ectopic expression of pSCR:GFP, respectively. Bars = 20 μm.