Tetraploidy  enhances the cold-resistance in yellow kiwifruit (Actinidia chinensis)

Abstract Yellow kiwifruit ( Actinidia chinensis ) is highly susceptible to severe weather, such as low temperature and frost, which may affect the production in the coming year. And the cold-resistant mechanism of kiwifruit associated with gene regulation is poorly investigated. To botain cold-resistant germplam, to provide insight into the causes of differences in low temperature tolerance due to ploidy and to better understand cold-adaptive mechanisms in tetraploid kiwifruit, the diploid yellow kiwifruit ‘SWFU03’ and its tetraploid plantlets were subjected to cold-tolerant screening with L-hydroxyproline (L-Hyp) and low temperature, the selected ones were then analyzed by transcriptome data and confirmed by RT-qPCR. The results showed that the survival rate of tetraploid plants was 62.22% when treated with 8 mmol/L L-Hyp for 30 days, while all the diploid ones died. After treated with 0°C for 12 h, then at room temperature for seven days, the survival rate of tetraploid plantlets was 42.22%, while all diploidy died. Hence, cold tolerance of the tetraploid plantlets was stronger than that of the diploid genotypes. Using these two screening systems, 126 cold-resistant tetraploid tissue culture plantlets were obtained. A total of 1630 differentially expressed genes (DEGs) were identified, of which 619 were up-regulated and 1011 were down-regulated in the low temperature treatment goup. The DEGs enriched in the cold-tolerance related pathways mainly included plant hormone signal transduction, and starch and sucrose metabolism pathway. RT-qPCR analysis confirmed the expression levels of eight up-regulated genes in these pathways in the cold-resistant mutants. In conclusion, this study has identified cold-resistant yellow kiwifruit plantlets and cold-tolerance related genes. Moreover, the dataset got in this study advances our knowledge of the cold-adaptive genes in the regulatory networks and leads to understand the cold tolerance mechanisms in the tetraploid yellow kiwifruit.