In kiwifruit (Actinidia arguta), fruit coloration is typically accompanied by ripening; however, the intrinsic connection between these two processes remains unclear. In this study, we found that ethylene and auxin accelerated and suppressed fruit coloration and ripening, respectively, in A. arguta. ETHYLENE INSENSITIVE 3-LIKE 2 (AaEIL2) and ETHYLENE RESPONSIVE FACTOR (AaERF059) were mined and identified using yeast two-hybrid library screening and transcriptome analysis. AaEIL2, specifically induced to high expression by ethylene, was confirmed as a transcription factor that positively regulates coloration and ripening by targeting AaLDOX (leucoanthocyanidin dioxygenase involved in anthocyanin biosynthesis) and AaPG18 (polygalacturonase involved in cell wall degradation) based on its subcellular localization in Arabidopsis protoplasts, stable genetic transformation in transgenic tomato, and yeast one-hybrid and luciferase activity assays. AaERF059 also responds to ethylene and regulates ethylene-/auxin-mediated fruit coloration and ripening by targeting the downstream genes AaACS2 (ACC synthase, which is involved in ethylene biosynthesis) and AaGH3 (Gretchen-Hagen 3, which is involved in the auxin pathway). Overall, AaEIL2 and AaERF059 regulate ethylene-and auxin-mediated fruit coloration and ripening by maintaining a dynamic balance in a positive and negative regulatory manner. Our results not only identified key genes but also established an intrinsic connection between fruit coloration and ripening in A. arguta.

Fruit quality traits play an important role in consumption of kiwiberry (Actinidia arguta). The genetic basis of fruit quality traits in this woody, perennial and dioecious fruit crop remains largely unknown. This study aimed to identify the underlying genetic basis of fruit quality traits in A. arguta, using a single nucleotide polymorphism (SNP) genetic linkage map previously developed in a tetraploid F₁ population of ‘Ruby-3’ × ‘KuiLv-M’. The F₁ population was phenotyped over three years (2020–2022) for fruit quality traits, including skin color, flesh color, fruit weight, fruit diameter, total soluble solids, fruit longitudinal diameter and fruit shape index. A total of nine QTLs were detected for five traits, explaining 10%–32% of the trait variation. For fruit color, the support interval of a major QTL on LG9 contained an MYB transcription factor MYB110, which was previously demonstrated to control color regulation in kiwifruit, thus suggesting that the MYB110 is the candidate gene for fruit color in kiwiberry. The linked marker for fruit color was validated in an F₁ population and 25 kiwiberry cultivars. In conclusion, the knowledge obtained through the QTL mapping is applicable to improve the efficiency and cost-effectiveness in kiwiberry breeding.

Waterlogging stress is one of the greatest environmental threats to kiwifruit growth and development. ERF-VⅡ proteins have been demonstrated to play pivotal roles in regulating plant tolerance to waterlogging. Nevertheless, the genome-wide role of ERF-VⅡ in kiwifruit waterlogging stress tolerance remains unclear. Here, we report the function and regulatory network of an ERF-VⅡ transcription factor located to the nucleus, AvERF73, in kiwifruit waterlogging tolerance. Overexpression of AvERF73 in Arabidopsis thaliana and A. chinensis cv. Hongyang enhanced waterlogging tolerance in transgenic plants. Furthermore, we performed transcriptome analysis (RNA-seq) and DNA affinity purification sequencing (DAP-seq) to explore the regulatory mechanism of AvERF73. RNA-seq coupled with DAP-seq showed that AvERF73 might directly activate AcNAC022 involved in the “cellular response to hypoxia” process and AcHMGS1 involved in the mevalonate pathway to respond to waterlogging, which were also confirmed by a dual-luciferase reporter assay. Based on our results, we propose a putative working model for controlling waterlogging tolerance by AvERF73 in kiwifruit.