Comprehensive analysis revealed that titanium dioxide nanoparticles could strengthen the resistance of apple rootstock B9 to saline-alkali stress.

Apple growth and development can be adversely affected by saline-alkali stress, which has become a significant factor restricting the high yield of the apple industry. In recent years, nanomaterials have become a potential source for plant growth and development. Titanium dioxide nanoparticles (TiO2 NPs) play an important role in multiple plant development processes, including mitigating environmental stress. In this study, one-year-old apple rootstock B9 stem cuttings were used as research objects. Different concentrations of TiO2 NPs were applied to the roots before saline-alkali treatment. Principal component analysis showed that 1gkg-1 TiO2 NPs treatment had the best effect in alleviating the stress for B9. It significantly reduced the damage to B9 under salt-alkali stress, increased the content of photosynthetic pigment, enhanced the performance of Photosystem II, and promoted photosynthesis. At the same time, the content of K+ was increased, and the ion toxicity was alleviated. In addition, TiO2 NPs have also been shown to reduce B9 cell damage and lipid peroxidation, increase antioxidant enzyme activity, and regulate the accumulation of solutes. Overall, this study provides a theoretical basis for TiO2 NPs to mitigate the adverse effects of plants under saline-alkali stress and provides useful insights for managing other plants affected by global salinity and alkalinity.

Transcription factors dealing with Iron-deficiency stress in plants: focus on the bHLH transcription factor family.

Iron (Fe), as an important micronutrient element necessary for plant growth and development, not only participates in multiple physiological and biochemical reactions in cells but also exerts a crucial role in respiration and photosynthetic electron transport. Since Fe is mainly present in the soil in the form of iron hydroxide, Fe deficiency exists universally in plants and has become an important factor triggering crop yield reduction and quality decline. It has been shown that transcription factors (TFs), as an important part of plant signaling pathways, not only coordinate the internal signals of different interaction partners during plant development, but also participate in plant responses to biological and abiotic stresses, such as Fe deficiency stress. Here, the role of bHLH transcription factors in the regulation of Fe homeostasis (mainly Fe uptake) is discussed with emphasis on the functions of MYB, WRKY and other TFs in the maintenance of Fe homeostasis. This review provides a theoretical basis for further studies on the regulation of TFs in Fe deficiency stress response.

Genome-wide identification of the CER1 gene family in apple and response of MdCER1-1 to drought stress.

Plant cuticular wax was a major consideration affecting the growth and quality of plants through protecting the plant from drought and other diseases. According to existing studies, CER1, as the core enzyme encoding the synthesis of alkanes, the main component of wax, can directly affect the response of plants to stress. However, there were few studies on the related functions of CER1 in apple. In this study, three MdCER1 genes in Malus domestica were identified and named MdCER1-1, MdCER1-2, and MdCER1-3 according to their distribution on chromosomes. Then, their physicochemical properties, sequence characteristics, and expression patterns were analyzed. MdCER1-1, with the highest expression level among the three members, was screened for cloning and functional verification. Real-time fluorescence quantitative PCR (qRT-PCR) analysis also showed that drought stress could increase the expression level of MdCER1-1. The experiment of water loss showed that overexpression of MdCER1-1 could effectively prevent water loss in apple calli, and the effect was more significant under drought stress. Meanwhile, MdYPB5, MdCER3, and MdKCS1 were significantly up-regulated, which would be bound up with waxy metabolism. Gas chromatography-mass spectrometer assay of wax fraction makes known that overexpression of MdCER1-1 apparently scaled up capacity of alkanes. The enzyme activities (SOD, POD) of overexpressed apple calli increased significantly, while the contents of proline increased compared with wild-type calli. In conclusion, MdCER1-1 can resist drought stress by reducing water loss in apple calli epidermis, increasing alkanes component content, stimulating the expression of waxy related genes (MdYPB5, MdCER3, and MdKCS1), and increasing antioxidant enzyme activity, which also provided a theoretical basis for exploring the role of waxy in other stresses.

Molecular cloning and functional characterization of MhHEC2-like genes in Malus halliana reveals it enhances Fe (iron) deficiency tolerance.

The basic helix-loop-helix (bHLH) family, as one of the largest families of transcription factors (TFs) in plants, plays crucial roles in regulating growth, development, and abiotic stress responses. However, studies on the association of the bHLH genes with apple iron (Fe) deficiency are limited. Here, multiple bHLH genes that responded to Fe deficiency were selected for quantitative real-time PCR in Malus halliana. The results showed that the expression of HEC2-like gene exerted more values compared to other genes under Fe deficiency stress, but the mechanism by which it regulates Fe deficiency stress is unclear. Subsequently, MhHEC2-like gene (ID: 103,455,961) was cloned from M. halliana for functional identification. We found that both transgenic Arabidopsis thaliana and tobacco displayed less chlorosis and more robust growth than wild-type (WT) controls under Fe deficiency stress. At the same time, the overexpressed apple calli grew prominently larger and better under Fe deficiency compared to the wild type. On the other hand, physiological index measurements revealed that overexpressed MhHEC2-like gene enhanced tolerance to Fe deficiency stress in A. thaliana and tobacco by promoting the synthesis of photosynthetic pigments, improving antioxidant enzyme activity, and enhancing Fe reduction, and strengthened tolerance to Fe deficiency stress in apple calli by reducing pH, boosting Fe reduction, and increasing antioxidant enzyme activity. To sum up, the overexpression of MhHEC2-like gene strengthened tolerance to Fe deficiency stress in Arabidopsis thaliana, tobacco, and apple calli.