Isolation and differential expression analysis of self-compatibility-related genes from mature pistils of ‘Shatangju’ mandarin (Citrus reticulata Blanco)

Abstract

SummaryThe objective of this research was to identify self-compatibility (SC)-related genes that are up-regulated in ‘Shatangju’ mandarin (Citrus reticulata Blanco). A suppression-subtractive hybridisation (SSH) cDNA library was constructed using self-compatible ‘Shatangju’ cDNA as the tester, and self-incompatible ‘Wuzishatangju’ mandarin cDNA as the driver. Among the 949 positive clones obtained in the size range of 200 – 700 bp, 158 showed up-regulated expression in ‘Shatangju’ mandarin. Several SC-related genes, such as those for the S1 self-incompatibility locus-linked pollen 3.15 protein (S1-protein), the ubiquitin-activating enzyme E1 (ubiquitin-E1), a zinc finger (C2H2 type) family protein (zinc-finger protein), the nuclear inhibitor of protein phosphatase-1 (nnpp-1), ubiquitin, molecular chaperones, and senescence-related proteins were identified. Semi-quantitative reverse transcription-PCR (sqRT-PCR) and quantitative real-time PCR (qPCR) were used in this study to elucidate the differential expression patterns of five of these SC-related genes. The results showed that expression levels of the S1-protein and of ubiquitin-E1 in ‘Shatangju’ ovaries and anthers were up-regulated by 60-fold and seven-fold, respectively, compared to the same tissues in ‘Wuzishatangju’ mandarin. The expression levels of the zinc-finger protein and the ubiquitin protein in ‘Shatangju’ leaves and buds were higher than in leaves and buds of ‘Wuzishatangju’. Expression levels of the nnpp-1 gene in the filaments and anthers of ‘Shatangju’ were three-fold and four-fold higher, respectively, than in the same tissues of ‘Wuzishatangju’. These results suggest that the S1-protein and ubiquitin-E1 might play an important role in the self-compatible reaction of ‘Shatangju’ mandarin. This information could provide new knowledge to understand SC, not only in citrus, but also in other fruit.