Ethylene‐activated MdPUB24 mediates ubiquitination of MdBEL7 to promote chlorophyll degradation in apple fruit

Abstract

SUMMARY Chlorophyll (Chl) degradation is a natural phenomenon that occurs during ripening in many fleshy fruit species, and also during fruit storage. The plant hormone ethylene is a key factor in promoting Chl degradation during fruit storage, but the mechanisms involved in this induction are largely unknown. In this study, an apple (Malus domestica) BEL1‐LIKE HOMEODOMAIN transcription factor 7 (MdBEL7), potentially functioning as a transcriptional repressor of the Chl catabolic genes (CCGs), including MdCLH, MdPPH2 and MdRCCR2, was identified as a partner of the ethylene‐activated U‐box type E3 ubiquitin ligase MdPUB24 in a yeast library screen. Yeast‐two‐hybrid, co‐immunoprecipitation and luciferase complementation imaging assays were then used to verify the interaction between MdBEL7 and MdPUB24. In vitro and in vivo ubiquitination experiments revealed that MdPUB24 functions as an E3 ubiquitin ligase to ubiquitinate MdBEL7, thereby causing its degradation through the 26S proteasome pathway. Transient overexpression of MdPUB24 in apple fruit led to a decrease in MdBEL7 abundance and increased expression of CCG genes, including MdCLH, MdPPH2 and MdRCCR2, as well as greater Chl degradation. Taken together, the data indicated that an ethylene‐activated U‐box type E3 ubiquitin ligase MdPUB24 directly interacts with and ubiquitinates MdBEL7. Consequent degradation of MdBEL7 results in enhanced expression of MdCLH, MdPPH2 and MdRCCR2, and thus Chl degradation during apple fruit storage. Our results reveal that an ethylene‐MdPUB24‐MdBEL7 module regulates Chl degradation by post‐translational modification during apple fruit storage.

Could Causal Discovery in Proteogenomics Assist in Understanding Gene–Protein Relations? A Perennial Fruit Tree Case Study Using Sweet Cherry as a Model

“…A characteristic paradigm was the transcription factors (TFs) PaBEL1H1; Pav_sc0000713.1_g640.1.mk and PaBEL1H9; Pav_sc0001794.1_g370.1.mk of ME27 that regulate chloroplast development and chlorophyll synthesis [ 35 ]. These TFs may influence PaBEL1H7; Pav_sc0001518.1_g260.1.mk of ME30 ( Figure 4 C) that were found to be involved in the chlorophyll degradation via ethylene production during fruit ripening [ 36 ]. The ME30 was characterized by the presence of FERONIA receptors since four of them (PaFERL; Pav_sc0000661.1_g020.1.br; Pav_sc0000681.1_g020.1.br; Pav_sc0004547.1_g070.1.br; Pav_sc0004547.1_g060.1.br) were contained in this module.…”

The Roles of BLH Transcription Factors in Plant Development and Environmental Response

“…Overexpressing the barley JuBEL1 in tobacco resulted in the phenomenon of reduced male fertility [ 90 ]. Apple MdBEL7 was degraded by ubiquitination, with the U-box E3 ubiquitin ligase MdPUB24, resulting in the degradation of chlorophyll in apple during storage [ 57 ]. In tomato, SIBEL11 and SlBL4 have been shown to be involved in regulating the development of chloroplasts and chlorophyll synthesis in tomato fruit [ 40 , 41 ] ( Figure 2 ).…”

“…In addition to transcriptional regulation, post-translational modifications play an important role in the regulatory network of transcription factors. Recent studies have shown that an E3 ubiquitin ligase (MdPUB24) in apple promotes the degradation of MdBEL7 and regulates the greening process of the apple fruit [ 57 ]. However, there are few studies on the post-translational modification of BLHs.…”

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

“…A recent study showed that PUB25 and PUB26 positively regulated the cold-stress response by mediating MYB15 protein degradation [ 81 ]. In apples, MdPUB24 and MdPUB29 regulate fruit quality [ 82 , 83 ]. In addition, MdPUB29 may also be involved in the regulation of the plant immune response to fungal pathogens [ 84 ].…”