RESUMO
Low temperatures can seriously affect apple yield and can also cause chilling injury to apple fruit. γ-aminobutyric acid (GABA) plays an important role in improving plant stress resistance. Some studies have reported that GABA can improve cold resistance in plants, only through exogenous treatment; however, the molecular mechanism of its resistance to low temperature is still unknown. This result suggested that exogenous GABA treatment of both apple seedlings and fruit could improve the resistance of apple to low temperatures. MdGAD1, a key gene involved in GABA synthesis, was overexpressed in tomato plants and apple callus to improve their cold tolerance. Both yeast one-hybrid and luciferase assay showed that MdCBF3 could bind to the MdGAD1 promoter to activate its expression and promote GABA synthesis. These results revealed a molecular mechanism utilizing the MdCBF3-MdGAD1 regulatory module that can enhance cold resistance by increasing endogenous GABA synthesis in apple.
RESUMO
Soil alkalization is an adverse factor limiting plant growth and yield. As a signaling molecule and secondary metabolite, γ-aminobutyric acid (GABA) responds rapidly to alkaline stress and enhances the alkaline resistance of plants. However, the molecular mechanisms by which the GABA pathway adapts to alkaline stress remain unclear. In this study, a transcription factor, MdNAC104 is identified, from the transcriptome of the alkaline-stressed roots of apple, which effectively reduces GABA levels and negatively regulates alkaline resistance. Nevertheless, applying exogenous GABA compensates the negative regulatory mechanism of overexpressed MdNAC104 on alkaline resistance. Further research confirms that MdNAC104 repressed the GABA biosynthetic gene MdGAD1/3 and the GABA transporter gene MdALMT13 by binding to their promoters. Here, MdGAD1/3 actively regulates alkaline resistance by increasing GABA synthesis, while MdALMT13 promotes GABA accumulation and efflux in roots, resulting in an improved resistance to alkaline stress. This subsequent assays reveal that MdSINA2 interacts with MdNAC104 and positively regulates root GABA content and alkaline resistance by ubiquitinating and degrading MdNAC104 via the 26S proteasome pathway. Thus, the study reveals the regulation of alkaline resistance and GABA homeostasis via the MdSINA2-MdNAC104-MdGAD1/3/MdALMT13 module in apple. These findings provide novel insight into the molecular mechanisms of alkaline resistance in plants.
RESUMO
Soil salinization had become a global ecological problem, which restricts the plant growth, and the quantity and quality of fruits. As a signaling molecule, γ-Aminobutyric acid (GABA) mediates a series of physiological processes and stress responses. Our previous research showed that GABA could alleviate drought, low phosphorus, cadmium stresses in apples, but the further research about its physiological mechanisms under salt stress was even more needed. The present study showed that the inhibition of salt stress on plant growth might be effectively alleviated by the treatment of 0.5 mM GABA, and the osmotic balance and photosynthetic capacity of plants could be maintained. Exogenous GABA could effectively inhibit the enrichment of reactive oxygen species and the uptake of Na+, while maintaining ion homeostasis. The experiment results indicated GABA could markedly promote the expression amount of Na+ and K+ transport-related genes (e.g., HKT1, AKT1, NHX1, SOS1, SOS2, and SOS3) in apples under salt stress. Overexpression and interference (RNAi) of MdGAD1 in apple roots, which is a crucial enzyme in the GABA biosynthesis, affected the salt tolerance of plants. Transgenic apple plants with roots of overexpression MdGAD1 showed less relative electrolyte leakage and more expression level of related ion transport genes than CK group, but RNAi MdGAD1 led to the opposite results. These results indicated that GABA accumulation could effectively strengthen the resistance of apple plants to salt stress and alleviate the injury of apple seedlings resulted from salinity.