Abstract
MdPG1 encoding polygalacturonase in apple (Malus × domestica) is a key gene associated with fruit firmness and texture variations among apple cultivars. However, the causative variants of MdPG1 are still not known. In this study, we identified a SNP(A/C) variant within an ERF-binding element located in the promoter region of MdPG1. The promoter containing the ERF-binding element with SNP(A), rather than the SNP(C), could be strongly bound and activated by MdCBF2, a member of the AP2/ERF transcription factor family, as determined by yeast-one-hybrid and dual-luciferase reporter assays. We also demonstrated that the presence of a novel long non-coding RNA, lncRNA(PG1), in the promoter of MdPG1 was a causative variant. lncRNA(PG1) was specifically expressed in fruit tissues postharvest. lncRNA(PG1) could reduce promoter activity when it was fused to the promoter of MdPG1 and a tobacco gene encoding Mg-chelatase H subunit (NtCHLH) in transgenic tobacco cells but could not reduce promoter activity when it was supplied in a separate gene construct, indicating a cis-regulatory effect. Our results provide new insights into genetic regulation of MdPG1 allele expression and are also useful for the development of elite apple cultivars.