A small molecule inhibits cell elongation by modulating cell wall polysaccharide composition in Arabidopsis

MYB transcription factor MdMYB44 positively regulates fruit crispness by directly activating the expression of pectin methylesterase MdMPE3 in apple

Crispness, a key attribute of fruit texture quality, is a critical determinant of apple commercial value. Pectin, a major component of the cell wall, plays a vital role in maintaining cell structure, turgor pressure, and mechanical support, with pectin methylesterase (PMEs, EC 3.1.1.11) mediating pectin modification during cell wall remodeling. In this study, we identified two genes, MdMYB44 and MdMPE3 (pectin methylesterase 3), that regulate apple fruit crispness. Through Y1H, EMSA, ChIP-qPCR, and transient expression assays, we demonstrated that the MYB transcription factor MdMYB44 directly enhances the expression of MdMPE3 by binding to its promoter. These results indicate that MdMYB44 acts as a positive regulator of fruit crispness by activating MdMPE3 transcription. Our findings provide new insights into the molecular mechanisms by which MYB transcription factors and pectin methylesterase influence apple fruit texture, enriching our understanding of the regulation of fruit crispness.

Differential pulp cell wall structures lead to diverse fruit textures in apple (Malus domestica)

In this study, we aimed to elucidate the effect of pulp cell wall structure on fruit hardness and crispness in apples. To this end, we studied the cell wall polysaccharides in two apple varieties, "Hanfu" and "Honeycrisp," during fruit development. Compared with Hanfu, the crispness of Honeycrisp was higher, whereas its harness was lower. The intensity and distribution of immunofluorescence signals indicated that galactose and arabinose contributed to the higher hardness of Hanfu, whereas arabinose, egg-box structure, and fucosylated xyloglucans, distributed in the corners of tricellular junctions, enhanced the cell-cell adhesion and improved the crispness of Honeycrisp. Besides, fucosylated xyloglucan played an important role in promoting the formation and maintaining the strength of the cell wall skeleton and, consequently, retaining the fruit crispness. The esterification state of pectin had little effect on the fruit hardness and crispness in both varieties. Collectively, our findings provided information on the underlying mechanism of fruit texture formation in apples.

Pear xyloglucan endotransglucosylase/hydrolases PcBRU1 promotes stem growth through regulating cell wall elongation

Brassinosteroids (BRs) play numerous important roles in plant growth and development. Previous studies reported that BRs could promote stem growth by regulating the expression of xyloglucan endotransglucosylase/hydrolases (XTHs). However, the mechanism of XTHs involved in stem growth remains unclear. In this study, PcBRU1, which belonged to the XTH family, was upregulated by exogenous BL treatment in Pyrus communis. The expression of PcBRU1 was highest in stems and lowest in leaves. Subcellular localization analysis indicated that PcBRU1 was located in the plasma membrane. Furthermore, overexpressing PcBRU1 in tobaccos promoted the plant height and internode length. Electron microscopy and anatomical structure analysis showed that the cell wall was significantly thinner and the cells were slenderer in transgenic tobacco lines overexpressing PcBRU1 than in wild-type tobaccos. PcBRU1 promoted stem growth as it loosened the cell wall, leading to the change in cell morphology. In addition, overexpressing PcBRU1 altered the root development and leaf shape of transgenic tobaccos. Taken together, the results could provide a theoretical basis for the XTH family in regulating cell-wall elongation and stem growth.