关键词: 柰李, 果实空腔褐变, 木质素生物合成, 酶活性, 4CL基因家族

Abstract:

【Objective】The objective of this study was to examine the temporal dynamics of hollowness and browning (HB) in Nai plum during its fruit development and ripening, to evaluate the relationship between HB and lignin accumulation, and to identify the 4CL gene family in Huangguan plum, a critical gene in the lignin biosynthetic pathway, at the whole-genome level. 【Method】Huangguan plum fruits were sampled at 10, 25, 40, 55, 70, and 80 days after full bloom to investigate the dynamics of HB. Anatomical changes in fruit structure induced by HB were observed by using paraffin sectioning. Lignin monomers were identified by using gas chromatography-mass spectrometry (GC-MS), while lignin content and associated enzyme activities were measured via UV-spectrophotometer. Gene expression was quantitatively analyzed through quantitative reverse transcription polymerase chain reaction (qRT-PCR). The genome-wide identification of the 4CL gene family was conducted utilizing tools, such as NCBI, TBtools, MEME, MEGA11, SOPMA, SWISS-MODEL, and PlantCARE. 【Result】HB initiated at the veraison stage, with the HB rate reaching 37.73% at the mature stage. Additionally, the fruit shape index of HB plum was significantly higher than that of non-HB plum. Histological analysis using paraffin section showed that the HB pulp was stained red by Saffron-O and Fast Green Stain and the HB area increased as the fruit developed. The total lignin content exhibited a gradual increase during fruit development and ripening, with the total lignin content in HB fruit being significantly higher than that in non-HB fruit (P≤0.001). The lignin monomers in HB fruit were predominantly composed of guaiacyl lignin (22.6%) and syringly lignin (10.8%). Both 4CL and PAL enzyme activities were significantly elevated in HB fruit compared with non-HB fruit during fruit development and ripening period. Expression levels of eight Ps4CLs were higher in HB fruit compared to non-HB fruit, with similar trends observed for two PsPALs which showed slightly higher expression in HB fruit during veraison stage. Ps4CL1, Ps4CL2, Ps4CL7, and Ps4CL8 were potentially implicated in the biosynthesis of lignin of plum fruit. The Ps4CL gene family characterized by a significant number of cis-acting elements associated with plant endogenous hormones. Collinearity analysis indicated the presence of two and eight pairs of 4CL homologous genes between plum and the Arabidopsis and peach, respectively. Weighted gene co-expression network analysis (WGCNA) identified core hub genes (Ps4CL5, Ps4CL7, and Ps4CL8), each exhibiting co-expression with at least 30 other genes. The qRT-PCR results demonstrated that Ps4CL genes exhibit tissue-specific and temporally specific expression profiles. 【Conclusion】This paper identified the critical period for HB occurrence (the veraison stage) and characterized the dynamics of lignin content, monomer type, enzyme activity, and related gene expression in Huangguan plum. WGNCA highlighted key genes involved in the lignin biosynthetic pathway in Huangguan plum, which laid a foundation for further exploration of regulatory mechanisms, control strategies, and related molecular mechanisms of HB in plum fruit.

Key words: plum, fruit hollowness and browning, lignin biosynthesis, enzyme activity, 4CL gene family