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Shoot shrivelling severely threatens growth and development of deciduous trees in the northern hemisphere, and we observed that there was a significant difference in shoot shrivelling rate between different apple varieties in practice. In this study, we investigated the anatomical and physiological characteristics of branches from different germplasm resources combined with an analysis of the transcriptome. Transcriptomes of samples treated in the initial dormancy, deep dormancy and freeze–thaw periods were generated and characterised. In three different periods, 7233 differentially expressed genes (DEGs) were identified including 3538 upregulated genes and 3695 downregulated genes. DEGs related to plant hormone signal transduction, starch and sucrose metabolism, cutin, suberin and wax biosynthesis were significantly enriched. Physiological characterisation showed that dormancy overwinter can induce the accumulation of soluble sugar and starch, shoot shrivelling rate of ‘Fuji’ was 2.31 times that of the ‘Delicious’; and the critical water content of ‘Delicious’ was significantly higher than ‘Fuji’. Phytohormone contents and proportions varied irregularly according to the overwintering phase among two varieties. Wax content, morphology and composition also exhibited difference. In conclusion, branch microstructure, phytohormone and wax metabolism all determined the overwintering performance of trees and phytohormones can regulate wax metabolism to ensure normal overwintering of trees.

Iron (Fe) deficiency is one of the most common micronutrient deficiencies limiting crop production globally, especially in arid regions because of decreased availability of iron in alkaline soils. S supply increases Fe availability to plants, ATP sulphatase plays an important role in the synthesis of organic sulfur in plants, which is considered to be an important rate-limiting enzyme in sulphur uptake. However, the mechanism of whether it responds to Fe deficiency in plants remains unclear. Here, we identified a ATP sulphatase gene MhATPS1 from Malus hallinan based on qRT-PCR and then genetically transformed it into tobacco and apple calli, which showed that transgenic tobacco and overexpressed apple calli secreted more H+ content compared to the wild type (WT), resulting in increased inter-root acidification. In addition, the transgenic tobacco and apple calli showed better growth under Fe deficiency conditions. Furthermore, increased Fe2+ content and ferric chelate reductase (FCR) activity in the transgenic tobacco and overexpressed calli indicated improved Fe uptake, which is also confirmed by up-regulation of Fe uptake genes, e.g. FRO2, IRT1, FER and FIT. Under Fe deficiency stress, having more strengthened antioxidant capacity in transgenic tobacco, and the same results were shown in overexpressed apple calli. At last, the NBT and DAB staining results also verified the greater scavenging capacity of reactive oxygen species in transgenic tobacco. In summary, the MhATPS1 gene may play a positive role in Fe deficiency stress both tobacco and apple calli.