Abstract:

In this study, we investigated the expression patterns of the MdACO1 gene and its transcription factor MdHB-1
in different organs at different developmental stages in apple, as well as their response to exogenous ethylene treatment,
with the purpose to reveal the relationship between these genes. The expression levels of MdACO1 and MdHB-1 in apple
cultivar “Royal Gala” were detected in different organs at different fruit development stages, also under exogenous ethylene
treatment by real-time quantitative PCR. Results showed that in different organs, MdHB-1 showed relatively higher
expression level in petal, while MdACO1 exhibited relatively high expression level in mature flesh. At the different stages
of fruit development, MdHB-1 gene was expressed highest in young flesh (about 40 days after the full flowering stage),
but MdACO1 gene exhihibited the highest expression level in mature fruits, specifically at 100 days after the full flowering
stage). Under exogenous ethylene treatment, the expression of MdHB-1 was inhibited in the fruits stored for 0–1 d, but its
expression level increased after 7 d storage, while the expression level of MdACO1 gene increased rapidly with the extension
of time. These results suggested that MdHB-1 may be involved in the regulation network of gene expression in young apple
fruits and floral organs, while MdACO1 was not involved in these processes. The MdACO1 gene played an important role in
the maturation of apple fruits, which was not regulated by MdHB-1. In addition, exogenous ethylene could induce the high
expression of MdACO1 in “Royal Gala”, while MdHB-1 did not participate in this feedback regulation process.

Key words: apple, ACO gene, transcription factor MdHB-1, expression patterns, ethylene