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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]

Background and aims: Jasmonate (JA) and ethylene are involved in the regulation of the aluminum (Al)-induced growth inhibition. Although it has been reported that JA enhances Al-induced root-growth inhibition, its role in the regulation of growth interplaying with ethylene is still not well understood. In this study, we investigated the mechanism underlying the effect of apple MdMYC2 transcription factor on Al stress. Methods: Overexpression lines were used for functional analysis. Real-time quantitative RT-PCR was used to examine the expression level of ethylene responsive genes. ChIP-PCR, EMSA, and Y1H assays were used to test whether MdMYC2-GST fusion protein could directly bind to MdERF3 promoter. Transient transactivation assays in tobacco leave were conducted to confirm whether MdMYC2 positively regulated the expression of MdERF3. Results: MdMYC2 negatively regulated Al tolerance with up-regulating the expression of ethylene responsive genes. Moreover, MdMYC2 was observed to bind to the promoter of MdERF3, a positive regulator of ethylene biosynthesis, and directly activated its transcription. And applying the antagonist of ethylene biosynthesis, AVG, alleviated MdMYC2-modulated growth inhibition in Al stress. Conclusions: We consider that MdMYC2 protein directly interacts and promotes the transcript of MdERF3 to affect ethylene biosynthesis, thereby regulating the Al-mediated stress response. Our findings provide a deeper understanding of the crosstalk between JA and ethylene as well as JA-mediated growth inhibition in apple. [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]

• MdCIB1interacts with MdCRY2 and participates in the regulation of flowering. • Overexpression of MdCIB1 enhances tolerance to PEG 6000 treatment. • Ectopic expression of MdCIB1 enhances drought stress tolerance. • MdCIB1 transgenic Arabidopsis alleviates ROS accumulation. Drought restricts the plant growth and productivity worldwide. The basic helix-loop-helix (bHLH) transcription factors play key roles in response to various abiotic stresses. In this study, we identified and characterized a bHLH transcription factor, cryptochrome-interacting bHLH 1 (MdCIB1), from apple (Malus domestica). MdCIB1 had a typical bHLH domain and was localized in the nucleus. Moreover, MdCIB1 also interacted with MdCRY2, and participated in blue light response and flowering time regulation. RT-qPCR analysis showed that PEG 6000 notably induced the transcript level of MdCIB1. MdCIB1 -overexpressing apple calli displayed improved tolerance to PEG 6000 treatment. Ectopic expression of MdCIB1 in Arabidopsis improved drought stress resistance, as reflected by better physiological indexes under drought stress, such as longer roots, higher chlorophyll levels and survival rate, and lower water loss rate of leaves than Col control. Further investigation demonstrated that MdCIB1 played a positive regulator in ABA sensitivity and ABA-mediated stomatal closure. In addition, MdCIB1 transgenic Arabidopsis exhibited higher proline content, lower malondialdehyde (MDA) content, and H 2 O 2 and O 2 − accumulation, as well as increased the activities of antioxidant enzymes under drought stress, which were able to protect plants from osmotic and oxidative damages. Besides, the transcripts of ROS scavenging-related genes and stress-responsive genes were also significantly upregulated in MdCIB1 transgenic lines. In summary, our study demonstrated that MdCIB1 plays a positive role in drought resistance. [ABSTRACT FROM AUTHOR]

• PEG 6000, NaCl, ABA and low temperature (4 °C) can induce the expression of MdGRF11. • Ectopic expression of MdGRF11 improves salt and drought tolerance. • Overexpression of MdGRF11 alleviates ROS accumulation. • MdGRF11 can interact with MdAREB/ABF transcription factors. The 14-3-3 proteins are a family of highly conserved phosphoserine-binding proteins that participate in the regulation of diverse physiological and developmental processes. In this research, twenty 14-3-3 genes in apples, which contained a highly conserved 14-3-3 domain, were identified and divided into two subgroups. Among them, MdGRF11 was further cloned and investigated. qRT-PCR analyses and GUS staining show that MdGRF11 is expressed in various organs and tissues with the highest expression levels found in the fruit. MdGRF11 was upregulated by polyethylene glycol 6000 (PEG 6000), NaCl, abscisic acid (ABA) and low temperature (4 °C) treatments. MdGRF11 -overexpressing transgenic Arabidopsis and apple calli exhibited reduced sensitivity to salt and PEG 6000 treatments. Moreover, the ectopic expression of MdGRF11 improved the tolerance of transgenic tobacco to salt and drought stresses, which grew longer roots, underwent more growth, and presented higher chlorophyll levels than the wild-type control under salt and drought stress conditions. Furthermore, MdGRF11 expression remarkably reduced electrolyte leakage, malondialdehyde content levels, H 2 O 2 and O2- accumulation under salt and drought stress conditions, which relied on the regulation of ROS-scavenging signaling to reduce oxidative damage of cells after salt and drought stress treatment. MdGRF11 also enhanced tolerance to stress by upregulating expression levels of ROS-scavenging and stress-related genes, especially improving responses to drought stress by modifying the water loss rates and stomatal aperture. Moreover, MdGRF11 could interact with MdAREB/ABF transcription factors through yeast two hybrid analyses. In conclusion, our results indicate that MdGRF11 acts as a positive regulator of salt and drought stress responses through regulating ROS scavenging and other signaling systems. [ABSTRACT FROM AUTHOR]