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The development of cold-tolerant varieties of winter turnip rape ( Brassica rapa L. ) is crucial for utilizing the potential of fallow land in northern China, enabling the cultivation of winter turnip rape as both a renewable energy crop and an industrial raw material. Antifreeze proteins (AFPs) play a crucial role in enhancing cold tolerance in plants by inhibiting the recrystallization and growth of ice crystals. In this study, AFPs or ice-binding proteins were isolated from the cold-tolerant variety Longyou 7 (L7) following cold treatment using the ice-crystal specific affinity adsorption method. The isolated protein inhibited ice recrystallization and modified the morphology of ice crystals. Mass spectrometry analysis revealed that this protein functions as an AFP in winter turnip rape, was designated as BrAFP2, and is classified as a thaumatin-like protein (TLP). The BrAFP2 gene and its promoter were cloned from 8 and 9 winter turnip rape cultivars, respectively. The multiple sequences alignment of the BrAFP2 coding region showed 9 single nucleotide polymorphisms (SNPs), including 2 sense mutations and 3 InDels, as well as 6 SNPs in the promoter. Under freezing conditions, the promoter activity was distinctly observed in leaves, calyxes, and silique pericarps, but not in roots. The analysis of the promoter using deletion fragments assay suggested that the core region of pBrAFP2 was included in a 336-bp fragment, from −879 to −453 away from the transcriptional start site (TSS), with this core fragment is required for transcriptional activity. The expression of BrAFP2 increased the cold tolerance in transgenic Arabidopsis lines. The two-hybrid assays in yeast and transiently transformed tobacco plants suggested that BrAFP2 may interact with a glutathione-S-transferase (BrGST). The interaction between BrGST and BrAFP2 may be associated with the maintenance BrAFP2 antifreeze action under low temperatures. These experimental results offer promise for the breeding of enhanced cold tolerance in winter turnip rape. • BrAFP2 inhibits ice recrystallization in cold-treated winter turnip rape. • The 336-bp fragment (-879 to −453) of the BrAFP2 promoter is essential for its transcription. • The interaction between BrAFP2 and BrGST likely enhances the cold tolerance of winter turnip rape.
Dong et al. (Wed,) studied this question.