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Abstract

The transition of stem cells from proliferation to differentiation is one of the most fundamental and important processes during development of multicellular organisms. Here we report that the bZIP transcription factor PERIANTHIA (PAN) plays a key role in controlling this transition in the shoot apical and floral meristems of Arabidopsis thaliana. Recently we could show that PAN promotes differentiation of floral stem cells by directly activating the homeotic patterning gene AGAMOUS (AG). Consistently, flowers of pan mutants grown in short days display indeterminacy and organ transformation defects similar to weak ag mutant flowers. Since PAN RNA is not confined to flowers, but also is detected in the center of the SAM in a region overlapping with the known stem cell regulators WUSCHEL (WUS) and CLAVATA3 (CLV3), we were interested to uncover its function in this tissue. We found that on the one hand PAN expression is dependent on the activity WUS, while at the same time WUS and CLV3 RNA accumulation is modified in pan mutants. Consistently, we identified components of the Cytokinin signaling system, which are known to be important for SAM function, acting downstream of PAN. Furthermore, PAN seems to be a target of Redox dependent posttranscriptional modification, while at the same time being involved in the transcriptional control of the Redox sensing system. Thus, PAN seems to be embedded into a complex regulatory network with inputs both at the transcriptional, as well as the posttranscriptional level. The redundant nature of the network might have concealed some functions of PAN so far, but combining classical genetics with tools of systems biology might allow us to dissect its important role in plant stem cell control.