College of Horticulture, State Key Laboratory of Crop Genetics & Germplasm Enhancement and Utilization, Nanjing Agricultural University, Nanjing, Jiangsu 210095, China.
The New Zealand Institute for Plant & Food Research Limited, Auckland 1025, New Zealand.
Plant Physiol. 2023 Jul 3;192(3):1997-2014. doi: 10.1093/plphys/kiad200.
Lignified stone cell content is a key factor used to evaluate fruit quality, influencing the economic value of pear (Pyrus pyrifolia) fruits. However, our understanding of the regulatory networks of stone cell formation is limited due to the complex secondary metabolic pathway. In this study, we used a combination of co-expression network analysis, gene expression profiles, and transcriptome analysis in different pear cultivars with varied stone cell content to identify a hub MYB gene, PbrMYB24. The relative expression of PbrMYB24 in fruit flesh was significantly correlated with the contents of stone cells, lignin, and cellulose. We then verified the function of PbrMYB24 in regulating lignin and cellulose formation via genetic transformation in homologous and heterologous systems. We constructed a high-efficiency verification system for lignin and cellulose biosynthesis genes in pear callus. PbrMYB24 transcriptionally activated multiple target genes involved in stone cell formation. On the one hand, PbrMYB24 activated the transcription of lignin and cellulose biosynthesis genes by binding to different cis-elements [AC-I (ACCTACC) element, AC-II (ACCAACC) element and MYB-binding sites (MBS)]. On the other hand, PbrMYB24 bound directly to the promoters of PbrMYB169 and NAC STONE CELL PROMOTING FACTOR (PbrNSC), activating the gene expression. Moreover, both PbrMYB169 and PbrNSC activated the promoter of PbrMYB24, enhancing gene expression. This study improves our understanding of lignin and cellulose synthesis regulation in pear fruits through identifying a regulator and establishing a regulatory network. This knowledge will be useful for reducing the stone cell content in pears via molecular breeding.
木质素石细胞含量是评估果实品质的关键因素，影响梨（Pyrus pyrifolia）果实的经济价值。然而，由于复杂的次生代谢途径，我们对石细胞形成的调控网络的理解有限。在这项研究中，我们使用了不同石细胞含量的梨品种的共表达网络分析、基因表达谱和转录组分析相结合的方法，鉴定了一个枢纽 MYB 基因 PbrMYB24。PbrMYB24 在果肉中的相对表达与石细胞、木质素和纤维素的含量显著相关。然后，我们通过同源和异源系统中的遗传转化验证了 PbrMYB24 调节木质素和纤维素形成的功能。我们构建了一个高效的梨愈伤组织木质素和纤维素生物合成基因验证系统。PbrMYB24 转录激活了多个参与石细胞形成的靶基因。一方面，PbrMYB24 通过与不同顺式元件（AC-I [ACCTACC] 元件、AC-II [ACCAACC] 元件和 MYB 结合位点（MBS）]）结合，激活木质素和纤维素生物合成基因的转录。另一方面，PbrMYB24 直接结合到 PbrMYB169 和 NAC STONE CELL PROMOTING FACTOR（PbrNSC）的启动子上，激活基因表达。此外，PbrMYB169 和 PbrNSC 均激活 PbrMYB24 的启动子，增强基因表达。本研究通过鉴定一个调控因子并建立调控网络，提高了我们对梨果实中木质素和纤维素合成调控的认识。这些知识将有助于通过分子育种减少梨果实中的石细胞含量。
