Identification of differentially expressed genes in 72 h styles from self-incompatible Citrus reticulata

• Two SSH libraries were constructed to isolate differentially expressed genes in 72 h styles from self-incompatibility Citrus reticulata.
• The expression characteristics of six SI candidate genes s are investigated.
• Up-regulated expression of six SI candidate genes was possibly involved in SI reaction of ‘Wuzishatangju’.

Self-incompatibility (SI) is one important factor that can result in seedless fruits of Citrus. Our previous study showed that ‘Wuzishatangju’ mandarin was gametophytic self-incompatibility (GSI) and 72 h was the crucial stage for the shift from a self-compatible to a self-incompatible state. However, it is not clear what genes are involved in the process. In this study, two SSH libraries were constructed to screen differentially expressed genes using 72 h styles after self-pollination of ‘Wuzishatangju’ and cross-pollination of ‘Wuzishatangju’ × ‘Shatangju’. 106 and 97 differentially expressed cDNA clones were sequenced and identified from forward and reverse SSH libraries, respectively. Differentially expressed ESTs are possibly involved in the SI reaction of ‘Wuzishatangju’ through S-phase kinase-associated protein1 (SKP1)-like activity, autoinhibited Ca2+-ATPase 1, U-box domain protein, and serine/threonine kinase. Results from quantitative real-time PCR (qPCR) showed that SKP1-like and U-box were obviously up-regulated in ovaries before pollination of ‘Wuzishatangju’, and approximately 20- and 2-fold higher than that of ‘Shatangju’, respectively. The SKP1-like and U-box were obviously up-regulated in pistils at 4 d after self-pollination of ‘Wuzishatangju’, and approximately 20- and 800-fold higher than that the same stage after cross-pollination of ‘Wuzishatangju’ × ‘Shatangju’, respectively. The potential involvement of these genes in the SI reaction is discussed.