School of Food and Biological Engineering, Hefei University of Technology, Hefei, 230009, China.
College of Horticulture Science and Engineering, State Key Laboratory of Crop Biology, Shandong Agricultural University, Tai'an, 271001, China.
BMC Plant Biol. 2022 Feb 17;22(1):71. doi: 10.1186/s12870-022-03453-8.
Calcium (Ca) deficiency can cause apple bitter pit, reduce the quality and shelf life. WRKY transcription factors play essential role in plant response to multiple disorders. However, the underlying mechanisms causing bitter pit in apple fruit due to Ca deficiency during storage is extremely limited.
In the present study, the nutritional metabolites and reactive oxygen species (ROS) were compared in Ca-deficient and healthy apple fruit (CK) during storage. Results showed that Ca-deficient apples sustained significantly higher production of ROS, PPO activity, flavonoids, total phenol, total soluble solids (TSS), and sucrose contents, but the contents of Ca, HO, titratable acids (TA), glucose and fructose were significantly lower than those of CK during storage. Principal component analysis (PCA) showed that TSS, •O, PPO, malondialdehyde (MDA) and Ca were the main factors, and TSS had a positive correlation with sucrose. Furthermore, transcriptome analysis revealed that WRKYs were co-expressed with sucrose metabolism-related enzymes (SWEETs, SS, SPS). qRT-PCR and correlation analysis indicated that MdWRKY75 was correlated positively with MdSWEET1. Moreover, transient overexpression of MdWRKY75 could significantly increase the sucrose content and promote the expression of MdSWEET1 in apple fruit.
Calcium deficiency could decrease antioxidant capacity, accelerate nutritional metabolism and up-regulate the expression of WRKYs in apple with bitter pit. Overexpression of MdWRKY75 significantly increased sucrose accumulation and the expression of MdSWEET1. These findings further strengthened knowledge of the basic molecular mechanisms in calcium deficiency apple flesh and contributed to improving the nutritional quality of apple fruit.
钙（Ca）缺乏会导致苹果苦痘病，降低果实品质和货架期。WRKY 转录因子在植物应对多种失调中起着重要作用。然而，由于贮藏过程中 Ca 缺乏导致苹果果实苦痘病的确切机制仍知之甚少。
本研究比较了贮藏过程中 Ca 缺乏和健康（CK）苹果果实的营养代谢物和活性氧（ROS）。结果表明，Ca 缺乏的苹果持续产生更高水平的 ROS、多酚氧化酶（PPO）活性、类黄酮、总酚、总可溶固形物（TSS）和蔗糖含量，但 Ca、HO、可滴定酸（TA）、葡萄糖和果糖含量明显低于 CK。主成分分析（PCA）表明，TSS、•O、PPO、丙二醛（MDA）和 Ca 是主要因素，TSS 与蔗糖呈正相关。此外，转录组分析表明，WRKYs 与蔗糖代谢相关酶（SWEETs、SS、SPS）共表达。qRT-PCR 和相关性分析表明，MdWRKY75 与 MdSWEET1 呈正相关。此外，瞬时过表达 MdWRKY75 可显著增加苹果果实中的蔗糖含量并促进 MdSWEET1 的表达。
Ca 缺乏可降低抗氧化能力，加速营养代谢，并上调苦痘病苹果中的 WRKYs 表达。过表达 MdWRKY75 可显著增加蔗糖积累和 MdSWEET1 的表达。这些发现进一步加强了对 Ca 缺乏苹果果肉基本分子机制的认识，有助于提高苹果果实的营养价值。
