Resman L, Howe G, Jonsen D, Englund M, Druart N. Schrader J, Antti H, Skinner J, Sjödin A, Chen T, Bhalerao RP
Components acting downstream of short day perception regulate differential cessation of cambial activity and associated response in early and late clones of hybrid Poplar
Plant Physiology: 2010 154:1294-1303

Abstract
Short days (SDs) in autumn induce growth cessation, bud set,cold acclimation, and dormancy in trees of boreal and temperateforests, and these responses occur earlier in northern thanin southern genotypes. Nevertheless, we know little about whetherthis variation results from differential perception of SDs ordifferential downstream responses to the SD signal or a combinationof the two. We compared global patterns of SD-regulated geneexpression in the stems of hybrid poplar (Populus trichocarpax Populus deltoides) clones that differ in their SD-inducedgrowth cessation in order to address this question. The timingof cessation of cambial cell division caused by SDs differedbetween the clones and was coincident with the change in thepattern of expression of the auxin-regulated genes. The clonesalso differed in the timing of their SD-regulated changes inthe transcript abundance of genes associated with cold tolerance,starch breakdown, and storage protein accumulation. By analyzingthe expression of homologs of FLOWERING LOCUS T, we demonstratedthat the clones differed little in their perception of SDs underthe growth conditions applied but differed substantially inthe downstream responses manifested in the timing and magnitudeof gene expression after SD treatment. These results demonstratethe existence of factors that act downstream of SD perceptionand can contribute to variation in SD-regulated adaptive photoperiodicresponses in trees.

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