Validation of MADS-box genes from apple fruit pedicels during early fruit abscission by transcriptome analysis and real-time PCR.

Abstract

Fruit abscission in an isolated region called abscission zone (AZ) is regulated by several genes including JOINTLESS, MACROCALYX and SEPALLATA, MADS-box genes, in tomato. The surviving central pedicels and the abscised lateral pedicels were examined in fruit clusters in order to investigate apple MADS-box genes from fruit pedicels of self-abscising apple 'Saika' during early fruit abscission. After performing RNA-Seq, transcription profiling was conducted on the MADS-box genes from apple central and lateral pedicels. The JOINTLESS homolog of apple (MdJOINTLESS) was amplified using degenerate primers annealing to a highly conserved domain based on the orthologous genes of various crops, including JOINTLESS gene of tomato. The expression pattern of MdJOINTLESS was investigated in central and lateral pedicles by real-time PCR. Some homologs were found which similar to JOINTLESS, MACROCALYX and SEPALLATA of tomato MADS-box genes from transcriptome analysis and RACE. Using phylogenetic analyses with the MADS-box gene family, MdJOINTLESS was classified into the SHORT VEGETATIVE PHASE (SVP) clade that included Arabidopsis and other crops. The expression level of MdJOINTLESS in central pedicel was more than twice as high as that of lateral pedicel. In the current study, we could find apple homologs of JOINTLESS, MACROCALYX, SEPALLATA, which were known to regulate pedicel AZ development in tomato. Furthermore, MdJOINTLESS might contribute to auxin gradation, influencing hierarchical ranking of auxin transport between fruit pedicels of self-abscising apple.