Fruit softening that occurs during fruit ripening and postharvest storage determines the fruit quality, shelf life and commercial value and makes fruits more attractive for seed dispersal. In addition, over-softening results in fruit eventual decay, render fruit susceptible to invasion by opportunistic pathogens. Many studies have been conducted to reveal how fruit softens and how to control softening. However, softening is a complex and delicate life process, including physiological, biochemical and metabolic changes, which are closely related to each other and are affected by environmental conditions such as temperature, humidity and light. In this review, the current knowledge regarding fruit softening mechanisms is summarized from cell wall metabolism (cell wall structure changes and cell-wall-degrading enzymes), plant hormones (ETH, ABA, IAA and BR et al.), transcription factors (MADS-Box, AP2/ERF, NAC, MYB and BZR) and epigenetics (DNA methylation, histone demethylation and histone acetylation) and a diagram of the regulatory relationship between these factors is provided. It will provide reference for the cultivation of anti-softening fruits.

The 26S proteasome is an ATP-dependent proteolytic complex in eukaryotes, which is mainly responsible for the degradation of damaged and misfolded proteins and some regulatory proteins in cells, and it is essential to maintain the balance of protein levels in the cell. The ubiquitin–26S proteasome pathway, which targets a wide range of protein substrates in plants, is an important post-translational regulatory mechanism involved in various stages of plant growth and development and in the maturation process of fleshy fruits. Fleshy fruit ripening is a complex biological process, which is the sum of a series of physiological and biochemical reactions, including the biosynthesis and signal transduction of ripening related hormones, pigment metabolism, fruit texture changes and the formation of nutritional quality. This paper reviews the structure of the 26S proteasome and the mechanism of the ubiquitin–26S proteasome pathway, and it summarizes the function of this pathway in the ripening process of fleshy fruits.

Polysaccharides from marine organisms have been extensively studied and utilized as functional food ingredients due to their excellent immunomodulatory properties. However, the immunomodulatory potential of fermented Ruditapes philippinarum polysaccharide (RPP) has not been systematically explored. This study investigated the effects of RPP on immune function in cyclophosphamide (CTX)-induced immunosuppressed BALB/c mice. These results revealed that RPP alleviated CTX-induced weight loss and restored appetite. Moreover, RPP can promote the morphology and indices of immune organs, as well as increased the number of white blood cells (WBC), red blood cells (RBC), and hemoglobin (Hb). Serum levels of interleukin-6 (IL-6) and immunoglobulin E (IgE) were significantly elevated following RPP treatment. Additionally, RPP improved colonic morphology by upregulating the expression of E-cadherin and ZO-1 and promoting the secretion of secretory IgA (sIgA). These results indicated that RPP exerted an immune protective effect in BALB/c mice and justified its further potential as a bioactive ingredient for functional foods derived from marine shellfish.