Transcripts Associated with Non-Acclimated Freezing Response in Two Barley Cultivars

Plants subjected to spring freezes are usually not acclimated sufficiently long to confer tolerance to sub-zero freezing stress in contrast to fall-grown plants which experience an acclimation period. Barley (Hordeum vulgare L.) periodically suffers from late spring freezes in areas throughout the world, with significant yield loss. We examined the response of 'Dicktoo' and 'Keunal' barley varieties to non-acclimated freezing (NAF) (-3 degrees C) at the jointing stage using the barley22K Affymetrix GeneChip to measure transcript abundances. Dicktoo was tolerant of NAF freezing for a longer period of time than Keunal, and had substantially more variable microarray probesets under the NAF treatment. Three hundred and thirteen probesets were selected as responsive genes to NAF based on their differential response in Dicktoo vs. Keunal. Seventy-one of these probesets had homology-based annotations, with 49 of them showing reduced transcript levels in Dicktoo NAF vs. Dicktoo control, Keunal control, and Keunal NAF treatments, and 22 showing increased transcript levels. Transcription factors, circadian related genes, and other genes involved in photoperiod response were represented among the probesets upregulated in Dicktoo NAF compared to Keunal NAF, while genes involved in RNA metabolism and water and sugar transport were downregulated. The transcriptome response of both Dicktoo and Keunal to NAF also differed from acclimation-based freezing treatments, with 43% of Dicktoo NAF and 37% of Keunal NAF probesets unique.