Effect of temperature on expression of B- and C-class MADS-box genes in flower buds of sweet cherry

Abstract

The occurrence of double fruits in sweet cherry (Prunus avium) is due to abnormal differentiation of pistil primordia in the previous growing season. Double pistil formation is caused by high temperature above 30°C during flower differentiation. Furthermore, extremely high temperature induces double pistil formation as well as homeotic transformation of stamens into pistil-like structures. Therefore, the B and C classes of homeotic genes, which control stamen and pistil formations, may be involved in these phenomena. In this study, we investigated the effect of temperature on the expression levels of B- and C-class MADS-box genes in flower buds. On July 20, when the buds had formed sepal and petal primordia, 'Satohnishiki' sweet cherry trees were brought into sunlit growth chambers with controlled temperatures at 25 and 35°C. Shortly after the onset of the treatment (3 and 10 days), spur buds were collected, and the expression levels of the APETALA3 (AP3)-like and PISTILLATA (PI)-like B-class genes and the AGAMOUS (AG)-like and SHATTERPROOF (SHP)-like C-class genes in the buds were analysed using real-time PCR. The transcriptional levels of PaTM6 (TM6 lineage of AP3) and PaAG at 35°C were much higher than those at 25°C. On the other hand, the high temperature considerably reduced the transcriptional levels of PaPI and PaSHP. We expected that increases in the expression level of C-class genes and decreases in that of B-class genes may be involved in double pistil formation and pistil-like stamens due to high temperature. However, only the changes in the expression levels of PaAG and PaPI genes were consistent with our expectations. Next, we plan to compare the expression levels of these genes among cultivars with different frequency of double pistils.