PT - JOURNAL ARTICLE AU - Trevor H. Yeats AU - Zoë Migicovsky AU - Sophie Watts AU - Jun Song AU - Charles F. Forney AU - Karen Burgher-MacLellan AU - Daryl J. Somers AU - Julia Vrebalov AU - James G. Giovannoni AU - Jocelyn K. C. Rose AU - Sean Myles TI - Allelic diversity of <em>NAC18.1</em> is a major determinant of fruit firmness and harvest date in apple (<em>Malus domestica</em>) AID - 10.1101/708040 DP - 2019 Jan 01 TA - bioRxiv PG - 708040 4099 - http://biorxiv.org/content/early/2019/07/20/708040.short 4100 - http://biorxiv.org/content/early/2019/07/20/708040.full AB - Softening is a hallmark of ripening in fleshy fruits, and has both desirable and undesirable implications for texture and postharvest stability. Accordingly, the timing and extent of ripening and associated textural changes are key targets for improving fruit quality through breeding. Previously, we identified a large effect locus associated with harvest date and firmness in apple (Malus domestica) using genome-wide association studies (GWAS). Here, we present additional evidence that polymorphisms in or around a transcription factor gene, NAC18.1, cause variation in these traits. First, we confirmed our previous findings with new phenotype and genotype data from ~800 apple accessions. In this population, we compared NAC18.1 to three other ripening-related markers currently used by breeders (ACS1, ACO1, and PG1), and found that the effect of the NAC18.1 genotype on both traits greatly exceeded that observed for the other markers. By sequencing NAC18.1 across 18 accessions, we revealed two predominant haplotypes containing the SNP previously identified using GWAS, as well as dozens of additional SNPs and indels in both the coding and promoter sequences. NAC18.1 encodes a protein with high similarity to the NON-RIPENING (NOR) transcription factor, an early regulator of ripening in tomato (Solanum lycopersicum). To test whether these genes are functionally orthologous, we introduced NAC18.1 transgenes into the tomato nor mutant and showed that both haplotypes complement the nor ripening deficiency. Taken together, these results indicate that polymorphisms in NAC18.1 underlie substantial variation in apple firmness and harvest time through modulation of a conserved ripening program.Highlight NAC18.1 is a member of a family of conserved transcriptional regulators of ripening that underlies variation in fruit firmness and harvest date in diverse apple accessions.