Transcriptome profiling of grapefruit flavedo following exposure to low temperature and conditioning treatments uncovers principal molecular components involved in chilling tolerance and susceptibility

A pre-storage conditioning (CD) treatment of 16 degrees C for 7 d enhanced chilling tolerance of grapefruit and reduced the development of chilling injuries during storage at 5 degrees C. To gain a better understanding of the molecular mechanisms involved in the responses of citrus fruit to low temperatures, we performed genome-wide transcriptional profiling analysis of RNA isolated from grapefruit flavedo using the newly developed Affymetrix Citrus GeneChip microarray. Utilizing very restrictive cut-off criteria, including pair-wise ANOVA comparisons significantly different at P <= 0.05 and induction or repression of transcript levels by at least fourfold, we found that out of 30 171 probe sets on the microarray, 1345 probe sets were significantly affected by chilling in both control and CD-treated fruits, 509 probe sets were affected by chilling specifically in the CD-treated fruits, and 417 probe sets were specifically expressed in chilling-sensitive control fruits. Overall, exposure to chilling led to expression arrest of general cellular metabolic activity, including concretive down-regulation of cell wall, pathogen defence, photosynthesis, respiration, and protein, nucleic acid and secondary metabolism. On the other hand, chilling enhanced adaptation processes that involve changes in the expression of transcripts related to membranes, lipid, sterol and carbohydrate metabolism, stress stimuli, hormone biosynthesis, and modifications in DNA binding and transcription factors.