Custom Microarray Analysis for Transcript Profiling of Dormant Vegetative Buds of Japanese Apricot during Prolonged Chilling Exposure

Bud dormancy is a critical developmental process for perennial plant survival, and also an important physiological phase that affects the next season’s growth of temperate fruit trees. Bud dormancy is regulated by multiple genetic factors, and affected by various environmental factors, tree age and vigor. To understand the molecular mechanism of bud dormancy in Japanese apricot (Prunus mume Sieb. et Zucc.), we constructed a custom oligo DNA microarray covering the Japanese apricot dormant bud ESTs referring to the peach (P. persica) genome sequence. Because endodormancy release is a chilling temperature-dependent physiological event, genes showing chilling-mediated differential expression patterns are candidates to control endodormancy release. Using the microarray constructed in this study, we monitored gene expression changes of dormant vegetative buds of Japanese apricot during prolonged artificial chilling exposure. In addition, we analyzed seasonal gene expression changes. Among the 58539 different unigene probes, 2345 and 1059 genes were identified as being more than twofold up-regulated and down-regulated, respectively, following chilling exposure for 60 days (P < 0.05). Cluster analysis suggested that the expression of the genes showing expression changes by artificial chilling exposure were coordinately regulated by seasonal changes. The down-regulated genes included P. mume DORMANCYASSOCIATED MADS-box genes, which supported previous quantitative RT-PCR and EST analyses showing that these genes are repressed by prolonged chilling exposure. The genes encoding lipoxygenase were markedly up-regulated by prolonged chilling. Our parametric analysis of gene-set enrichment suggested that genes related to jasmonic acid (JA) and oxylipin biosynthesis and metabolic processes were significantly up-regulated by prolonged chilling, whereas genes related to circadian rhythm were significantly down-regulated. The results obtained from microarray analyses were verified by quantitative RT-PCR analysis of selected genes. Taken together, we have concluded that the microarray platform constructed in this study is applicable for deeper understanding of the molecular network related to agronomically important bud physiology, including dormancy release.