Apple U-box-type E3 ubiquitin ligase MdPUB23 reduces cold-stress tolerance by degrading the cold-stress regulatory protein MdICE1.

Cold stress limits plant growth, geographical distribution, and crop yield. The MYC-type bHLH transcription factor ICE1 is recognized as the core positive regulator of the cold-stress response. However, how ICE1 protein levels are regulated remains to be further studied.

Apple SINA E3 ligase MdSINA3 negatively mediates JA-triggered leaf senescence by ubiquitinating and degrading the MdBBX37 protein.

Jasmonic acid (JA) induces chlorophyll degradation and leaf senescence. B-box (BBX) proteins play important roles in the modulation of leaf senescence, but the molecular mechanism of BBX protein-mediated leaf senescence remains to be further studied. Here, we identified the BBX protein MdBBX37 as a positive regulator of JA-induced leaf senescence in Malus domestica (apple).

The SUMO E3 Ligase MdSIZ1 Sumoylates a Cell Number Regulator MdCNR8 to Control Organ Size.

Plant growth and organ size putatively associated with crop yield are regulated by a complex network of genes including ones for controlling cell proliferation. The gene was first identified in tomatoes and reported to govern fruit size variation through controlling cell division. In this study, we isolated a putative ortholog of the tomato gene from apple, ().

Organization and regulation of the apple SUMOylation system under salt and ABA.

Small ubiquitin-related modifier (SUMO)-mediated post-translational protein modification is widely conserved among eukaryotes. SUMOylation refers to the covalent attachment of SUMO to target proteins that alters their function, location, and protein-protein interactions when plants are under abiotic stress. We identified 37 genes in the apple genome that encoded members of the SUMOylation pathway.

Phytochrome interacting factor MdPIF7 modulates anthocyanin biosynthesis and hypocotyl growth in apple.

Light affects many physiological and developmental processes of plants by regulating the expression and activity of light-responsive proteins. Among them, phytochrome interacting factors (PIFs) play pivotal roles in the regulation of anthocyanin accumulation and hypocotyl growth. However, the molecular mechanism is not well understood, especially in woody plants, such as apple (Malus × domestica).

Abscisic acid insensitive 4 interacts with ICE1 and JAZ proteins to regulate ABA signaling-mediated cold tolerance in apple.

Abscisic acid is involved in the regulation of cold stress response, but its molecular mechanism remains to be elucidated. In this study, we demonstrated that the APETALA2/ethylene responsive factor (AP2/ERF) family protein MdABI4 positively regulates abscisic acid-mediated cold tolerance in apple. We found that MdABI4 interacts with MdICE1, a key regulatory protein involved in the cold stress response, and enhances the transcriptional regulatory function of MdICE1 on its downstream target gene MdCBF1, thus improving abscisic acid-mediated cold tolerance.

Apple SUMO E3 ligase MdSIZ1 facilitates SUMOylation of MdARF8 to regulate lateral root formation.

Post-translational modification of proteins mediated by SIZ1, a small ubiquitin-like modifier (SUMO) E3 ligase, regulates multiple biological processes in plants. However, its role in the regulation of lateral root formation remains unclear. Here, we demonstrate that the apple SUMO E3 ligase MdSIZ1 promotes lateral root formation.

An apple long-chain acyl-CoA synthetase 2 gene enhances plant resistance to abiotic stress by regulating the accumulation of cuticular wax.

Apple cuticular wax can protect plants from environmental stress, determine fruit luster and improve postharvest fruit storage quality. In recent years, dry weather, soil salinization and adverse environmental conditions have led to declines in apple fruit quality. However, few studies have reported the molecular mechanisms of apple cuticular wax biosynthesis.

An apple long-chain acyl-CoA synthetase, MdLACS4, induces early flowering and enhances abiotic stress resistance in Arabidopsis.

The aerial parts of apple are protected against environmental stress by cuticular wax. Although it has been suggested that several long-chain acyl-CoA synthetases are involved in wax biosynthesis, the molecular pathway of apple cuticular wax biosynthesis remains unclear. In this study, an MdLACS4 protein with long-chain acyl-CoA synthetase activity was isolated from apple.

The R2R3 MYB transcription factor MdMYB30 modulates plant resistance against pathogens by regulating cuticular wax biosynthesis.

Background: The MYB transcription factor family is one of the largest transcriptional factor families in plants and plays a multifaceted role in plant growth and development. However, MYB transcription factors involved in pathogen resistance in apple remain poorly understood.

Results: We identified a new MYB family member from apple, and named it MdMYB30.

Apple AP2/EREBP transcription factor MdSHINE2 confers drought resistance by regulating wax biosynthesis.

This study showed that AP2/EREBP transcription factor MdSHINE2 functioned in mediating cuticular permeability, sensitivity to abscisic acid (ABA), and drought resistance by regulating wax biosynthesis. Plant cuticular wax plays crucial roles in protecting plants from environmental stresses, particularly drought stress. Many enzymes and transcription factors involved in wax biosynthesis have been identified in plant species.

The SUMO E3 Ligase MdSIZ1 Targets MdbHLH104 to Regulate Plasma Membrane H-ATPase Activity and Iron Homeostasis.

SIZ1 (a SIZ/PIAS-type SUMO E3 ligase)-mediated small ubiquitin-like modifier (SUMO) modification of target proteins is important for various biological processes related to abiotic stress resistance in plants; however, little is known about its role in resistance toward iron (Fe) deficiency. Here, the SUMO E3 ligase MdSIZ1 was shown to be involved in the plasma membrane (PM) H-ATPase-mediated response to Fe deficiency. Subsequently, a basic helix-loop-helix transcription factor, MdbHLH104 (a homolog of Arabidopsis bHLH104 in apple), which acts as a key component in regulating PM H-ATPase-mediated rhizosphere acidification and Fe uptake in apples (), was identified as a direct target of MdSIZ1.

Genome-wide identification and characterization of apple long-chain Acyl-CoA synthetases and expression analysis under different stresses.

Long-chain acyl-CoA synthetases (LACSs) are members of the acyl-activating enzyme superfamily that have important roles in lipid synthesis and storage, fatty acid catabolism, vectorial acylation, and synthesis of cutin and wax. Here, 11 apple MdLACS genes were identified based on the Malus × domestica reference genome, clustered into six groups and mapped to ten chromosomes. Multiple sequence alignment and conserved motifs analyses showed that the sequences of the AtLACS and MdLACS proteins were highly conserved.