Search

SUMMARY: Watercore is a common physiological disease of Rosaceae plants, such as apples (Malus domestica), usually occurring during fruit ripening. Apple fruit with watercore symptoms is prone to browning and rotting, thus losing commercial viability. Sorbitol and calcium ions are considered key factors affecting watercore occurrence in apples. However, the mechanism by which they affect the occurrence of watercore remains unclear. Here, we identified that the transcription factor MdWRKY9 directly binds to the promoter of MdSOT2, positively regulates the transcription of MdSOT2, increases sorbitol content in fruit, and promotes watercore occurrence. Additionally, MdCRF4 can directly bind to MdWRKY9 and MdSOT2 promoters, positively regulating their expression. Since calcium ions can induce the ubiquitination and degradation of the transcription factor MdCRF4, they can inhibit the transcription of MdWRKY9 and MdSOT2 by degrading MdCRF4, thereby reducing the sorbitol content in fruit and inhibiting the occurrence of fruit watercore disease. Our data sheds light on how calcium ions mitigate watercore in fruit, providing molecular‐level insights to enhance fruit quality artificially. [ABSTRACT FROM AUTHOR]

Summary: Nitric oxide (NO) is known to modulate the action of several phytohormones. This includes the gaseous hormone ethylene, but the molecular mechanisms underlying the effect of NO on ethylene biosynthesis are unclear.Here, we observed a decrease in endogenous NO abundance during apple (Malus domestica) fruit development and exogenous treatment of apple fruit with a NO donor suppressed ethylene production, suggesting that NO is a ripening suppressor.Expression of the transcription factor MdERF5 was activated by NO donor treatment. NO induced the nucleocytoplasmic shuttling of MdERF5 by modulating its interaction with the protein phosphatase, MdPP2C57. MdPP2C57‐induced dephosphorylation of MdERF5 at Ser260 is sufficient to promote nuclear export of MdERF5. As a consequence of this export, MdERF5 proteins in the cytoplasm interacted with and suppressed the activity of MdACO1, an enzyme that converts 1‐aminocyclopropane‐1‐carboxylic acid (ACC) to ethylene. The NO‐activated MdERF5 was observed to increase in abundance in the nucleus and bind to the promoter of the ACC synthase gene MdACS1 and directly suppress its transcription.Together, these results suggest that NO‐activated nucleocytoplasmic MdERF5 suppresses the action of ethylene biosynthetic genes, thereby suppressing ethylene biosynthesis and limiting fruit ripening. [ABSTRACT FROM AUTHOR]

Ethylene is one of the most important plant hormones involved in the climacteric fruit ripening process. Apple is a climacteric fruit, and its ripening process is regulated by ethylene. The effect of light-emitting diode (LED) light on plant growth and development has been extensively investigated; however, it remains unclear how LED light affects apple fruit ripening. Herein, we observed that the ripening of apple fruit treated with eight kinds of LED light was significantly inhibited compared with that of the dark control, with inhibition by white light being the most significant. Furthermore, the optimal light intensity for the inhibition of ethylene production was 20 μmol·m−2s−1, with an optimal light duration of 12 h per day. LED white light treatment enhanced the expression of two ELONGATED HYPOCOTYL 5 (HY5) genes, MdHY5L and MdHY5S , which encode transcription factors involved in the light signaling pathway. These two HY5s inhibited the transcription of MdACS1 , a crucial rate-limiting enzyme in the ethylene synthesis pathway, by directly binding to its promoter. Collectively, these findings imply that LED white light induces the expression of MdHY5L and MdHY5S and delays the expression of the ethylene synthesis-related gene MdACS1 to prevent fruit ripening. This study preliminarily elucidates the molecular mechanism underlying LED white light-induced inhibition of ethylene synthesis in apple fruit, providing an important theoretical basis for studying how to improve the storage ability and prolong the shelf life of apple fruit. • LED white light inhibits ethylene biosynthesis during apple fruit ripening. • LED white light induced the expression of MdHY5L / S. • MdHY5 binds to the promoter of MdACS1 and downregulates its expression. [ABSTRACT FROM AUTHOR]