Variation in flower frost tolerance among seven apple cultivars and transcriptome response patterns in two contrastingly frost-tolerant selected cultivars

This study evaluated frost tolerance in flowers of seven major apple cultivars grown in Korea to develop frost-resistant varieties for sustainable apple production under climate change. Flowers at full bloom were exposed to simulated frost conditions at -2°C, and frost damage was assessed using the total flower frost damage rate and King flower frost damage rate. Over 3 years, "Arisoo" consistently exhibited strong frost tolerance, whereas 'Fuji' was frost-sensitive. Transcriptomic analysis revealed significant differences in gene expression both within cultivars under different treatments and between cultivars under identical conditions. A higher number of differentially expressed genes were upregulated under frost stress in both cultivars, indicating key regulatory mechanisms involved in frost adaptation. Functional annotation and Kyoto Encyclopedia of Genes and Genome pathway analysis identified plant hormone signaling, mitogen-activated protein kinase signaling, and starch and sucrose metabolism can contribute to frost tolerance. Our findings offer critical insights into the genetic and molecular mechanisms of frost tolerance, contributing to the development of resilient apple varieties and sustainable production systems under climate change.