The cold-induced factor CBF3 mediates root stem cell activity,regeneration,and developmental responses to cold

Plant growth and development involve the specification and regeneration of stem cell niches(SCNs).Although plants are exposed to disparate environmental conditions,how environmental cues affect developmental programs and stem cells is not well understood.Root stem cells are accommodated in meristems in SCNs around the quiescent center(QC),which maintains their activity.Using a combination of genetics and confocal microscopy to trace morphological defects and correlate them with changes in gene expression and protein levels,we show that the cold-induced transcription factor(TF)C-REPEAT BINDING FACTOR 3(CBF3),which has previously been associated with cold acclimation,regulates root development,stem cell activity,and regeneration.CBF3 is integrated into the SHORT-ROOT(SHR)regulatory network,forming a feedback loop that maintains SHR expression.CBF3 is primarily expressed in the root endodermis,whereas the CBF3 protein is localized to other meristematic tissues,including root SCNs.Complementation of cbf3-1 using a wild-type CBF3 gene and a CBF3 fusion with reduced mobility show that CBF3 movement capacity is required for SCN patterning and regulates root growth.Notably,cold induces CBF3,affecting QC activity.Furthermore,exposure to moderate cold around 10℃–12℃promotes root regeneration and QC respecification in a CBF3-dependent manner during the recuperation period.By contrast,CBF3 does not appear to regulate stem cell survival,which has been associated with recuperation from more acute cold(-4℃).We propose a role for CBF3 in mediating the molecular interrelationships among the cold response,stem cell activity,and development.

Regulation of the New Arabidopsis Imprinted Gene AtBMI1C Requires the Interplay of Different Epigenetic Mechanisms

Recently, it has been shown that plants contain homologs to the animal Polycomb repressive complex I （PRC1） components BM11 and RINGIA/B. In Arabidopsis, there are three BMIl-like genes, two of which, AtBMIIA and B, are required during post-embryonic plant growth to repress embryonic traits and allow cell differentiation. However, little is known about the third BMIl-like gene, AtBMIIC. In this work, we show that AtBMIIC is only expressed during endosperm and stamen development. AtBMIIC is an imprinted gene expressed from the maternal allele in the endosperm but bialleli- cally expressed in stamen. We found that the characteristic expression pattern of AtBMIIC is the result of a complex epigenetic regulation that involves CG DNA methylation, RNA-directed non-CG DNA methylation （RdDM）, and PcG activity. Our results show the orchestrated interplay of different epigenetic mechanisms in regulating gene expression throughout development, shedding light on the current hypotheses for the origin and mechanism of imprinting in plant endosperm.