Comparative transcript profiling of gene expression between self-incompatible and self-compatible mandarins by suppression subtractive hybridization and cDNA microarray

Self-incompatibility (SI) is an important trait of Citrus plants that is exploited by farmers to produce seedless fruit. However, the molecular mechanism of SI in Citrus is not well understood. Wuzishatangju (Citrus reticulata Blanco) (SI) is an excellent seedless cultivar selected from a seedy Shatangju cultivar (self-compatible, SC) through spontaneous bud mutation. The two cultivars are therefore excellent materials for studying the mechanisms of SI and/or SC in Citrus. In this study, an integrative strategy combining eight suppression subtractive hybridization libraries with cDNA microarray was used to study the molecular mechanisms that differ between Wuzishatangju and Shatangju (control) mandarins. A custom microarray screen resulted in a total of 1,830 up-or down-regulated clones (false discovery rate <0.05 and a fold change >= 2) obtained from 9,810 positive clones. The expression of genes involved in embryonic development, ubiquitination pathway, Ca2+-signaling pathway, gibberellins, and auxin was significantly upregulated in SI Wuzishatangju compared with SC Shatangju mandarin. The microarray analysis suggested that the ubiquitin-mediated proteolysis pathway might be involved in the SI reaction of Wuzishatangju. Additionally, our research highlighted some main genes (mitogen-activated protein kinase, SI S1 family protein, ubiquitin-conjugating factor E4-like, auxin transporter protein 1, and gibberellin receptor) that participate in the SI reaction of Wuzishatangju and could be beneficial for understanding the evolution of SI systems and for breeding seedless citrus fruits in the future.