Transcriptional Analysis Provides New Insights into Cold- and Dehydration-Tolerance Signaling Pathways and on Regulation of Stem Cell Activity in the Vascular Cambium of Poplar

Stem cells play a critical role in the regulation of plant growth and development. Vascular cambium is the lateral meristem, producing secondary vascular elements in trees. Poplar cambium arrests growth at the onset of winter in northern climates to prevent freezing-related damage. We used cryosectioning and laser microdissection to isolate dormant and active cambium cells from stems of the poplar clone Nanlin 95 for transcriptome-wide analysis using the Affymetrix Poplar Genome Array. We observed that genes predicted to participate in systemic interaction with the environment performed well in dormant cambium and genes about cell cycle and DNA processing did well in active cambium. The dormant cambium was characterized by the upregulation of pathways controlling the expression of several cold- and dehydration-induced transcripts, resemble stress response signaling pathways characterized in Arabidopsis thaliana. The expression of PeWOX4, PeCLE41/44, and PeTDR/PXY suggests the existence of a system that maintains the cambium by enhancing proliferation, whereas the detection of transcripts of CLV3-like genes indicates the existence of a pathway that involves PeCLE12, PeCLE13 or PeCLE25, and PeWOX4 to promote the differentiation of stem cells in the poplar vascular cambium, much like the system of WUS (WUSCHEL)-CLV (CLAVATA) which promote differentiation in the shoot apical meristem of Arabidopsis.