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Key message: Ectopic expression of MmCYP1A1 gene from Mus musculus in apple calli and Arabidopsis increased the levels of melatonin and 6-hydroxymelatonin, and improved their stress resistance. Melatonin occurs widely in organisms, playing a key regulatory role. CYP1A1 is a cytochrome P450 monooxygenase, involved in the melatonin metabolism, and is responsible for the synthesis of 6-hydroxymelatonin from melatonin. Melatonin and 6-hydroxymelatonin have strong antioxidant activities in animals. Here, we cloned MmCYP1A1 from Mus musculus and found that ectopic expression of MmCYP1A1 improved the levels of melatonin and 6-hydroxymelatonin in transgenic apple calli and Arabidopsis. Subsequently, we observed that MmCYP1A1 increased the tolerance of transgenic apple calli and Arabidopsis to osmotic stress simulated by polyethylene glycol 6000 (PEG 6000), as well as resistance of transgenic Arabidopsis to drought stress. Further, the number of lateral roots of MmCYP1A1 transgenic Arabidopsis were enhanced significantly after PEG 6000 treatment. The expression of MmCYP1A1 remarkably reduced malondialdehyde (MDA) content, electrolyte leakage, accumulation of H2O2 and O2− during stress treatment. Moreover, MmCYP1A1 enhanced stress tolerance in apple calli and Arabidopsis by increasing the expression levels of resistance genes. MmCYP1A1 also promoted stomatal closure in transgenic Arabidopsis to reduce leaf water loss during drought. Our results indicate that MmCYP1A1 plays a key role in plant stress tolerance, which may provide a reference for future plant stress tolerance studies. [ABSTRACT FROM AUTHOR]

Fe deficiency is a widespread nutritional disorder in plants. The basic helix-loop-helix ( bHLH) transcription factors ( TFs), especially Ib subgroup bHLH TFs which are involved in iron uptake, have been identified. In this study, an IVc subgroup bHLH TF Mdb HLH104 was identified and characterized as a key component in the response to Fe deficiency in apple. The overexpression of the Mdb HLH104 gene noticeably increased the H+- ATPase activity under iron limitation conditions and the tolerance to Fe deficiency in transgenic apple plants and calli. Further investigation showed that Mdb HLH104 proteins bonded directly to the promoter of the Md AHA8 gene, thereby positively regulating its expression, the plasma membrane ( PM) H+- ATPase activity and Fe uptake. Similarly, Mdb HLH104 directly modulated the expression of three Fe-responsive bHLH genes, Mdb HLH38, Mdb HLH39 and Md PYE. In addition, Mdb HLH104 interacted with 5 other IVc subgroup bHLH proteins to coregulate the expression of the Md AHA8 gene, the activity of PM H+- ATPase and the content of Fe in apple calli. Therefore, Mdb HLH104 acts together with other apple bHLH TFs to regulate Fe uptake by modulating the expression of the Md AHA8 gene and the activity of PM H+- ATPase in apple. [ABSTRACT FROM AUTHOR]