SummaryThe Arabidopsis trichome is a model system for studying cell development, cell differentiation and the cell cycle in plants. Our previous studies have shown that the ZINC FINGER PRO-TEIN5 (ZFP5) controls shoot maturation and epidermal cell fate through GA signaling in Arabidopsis.We have identified a novel C2H2 zinc finger protein ZINC FINGER PROTEIN 6 (ZFP6) which plays a key role in regulating trichome development in Arabidopsis.Overexpression of ZFP6 results in ectopic trichomes on carpels and other inflorescence organs. Gain-and loss-of-function analyses have shown that the zfp6 mutant exhibits a reduced number of trichomes in sepals of flowers, cauline leaves, lateral branch and main inflorescence stems in comparison to wild-type plants.Molecular and genetic analyses suggest that ZFP6 functions upstream of GIS, GIS2, ZFP8, ZFP5 and key trichome initiation regulators GL1 and GL3.We reveal that ZFP6 and ZFP5 mediate the regulation of trichome initiation by integrating GA and cytokinin signaling in Arabidopsis. These findings provide new insights into the molecular mechanism of plant hormone control of epidermal trichome patterning through C2H2 transcriptional factors.

Arabidopsis (Arabidopsis thaliana) trichome development is a model system for studying cell development, cell differentiation, and the cell cycle. Our previous studies have shown that the GLABROUS INFLORESCENCE STEMS (GIS) family genes, GIS, GIS2, and ZINC FINGER PROTEIN8 (ZFP8), control shoot maturation and epidermal cell fate by integrating gibberellins (GAs) and cytokinin signaling in Arabidopsis. Here, we show that a new C2H2 zinc finger protein, ZFP5, plays an important role in controlling trichome cell development through GA signaling. Overexpression of ZFP5 results in the formation of ectopic trichomes on carpels and other inflorescence organs. zfp5 loss-of-function mutants exhibit a reduced number of trichomes on sepals, cauline leaves, paraclades, and main inflorescence stems in comparison with wild-type plants. More importantly, it is found that ZFP5 mediates the regulation of trichome initiation by GAs. These results are consistent with ZFP5 expression patterns and the regional influence of GA on trichome initiation. The molecular analyses suggest that ZFP5 functions upstream of GIS, GIS2, ZFP8, and the key trichome initiation regulators GLABROUS1 (GL1) and GL3. Using a steroid-inducible activation of ZFP5 and chromatin immunoprecipitation experiments, we further demonstrate that ZFP8 is the direct target of ZFP5 in controlling epidermal cell differentiation.Cell differentiation and morphogenesis at appropriate times and places are critical for the normal development of multicellular organisms (Ishida et al., 2008).

). † These authors contributed equally to this work. SUMMARYAlthough root hair development in Arabidopsis thaliana has been extensively studied, it remains unknown whether the zinc finger proteins, the largest family of transcription factors in plants, are involved in this process. Here we report that the C2H2 zinc finger protein ZINC FINGER PROTEIN 5 (ZFP5) is a key regulator of root hair initiation and morphogenesis in Arabidopsis. ZFP5 is mainly expressed in root and preferentially in root hair cells. Using both zfp5 mutants and ZFP5 RNAi lines, we show that reduction in ZFP5 function leads to fewer and much shorter root hairs compared to wild-type. Genetic and molecular experiments demonstrate that ZFP5 exerts its effect on root hair development by directly promoting expression of the CAPRICE (CPC) gene. Furthermore, we show that ZFP5 expression is induced by cytokinin, and that ZFP5 mediates cytokinin and ethylene effects on the formation and growth of root hairs. These results suggest that ZFP5 integrates various plant hormone cues to control root epidermal cell development in Arabidopsis.