PbAGL7-PbNAC47-PbMYB73 complex coordinately regulates PbC3H1 and PbHCT17 to promote the lignin biosynthesis in stone cells of pear fruit.

Lignification of the cell wall in pear (Pyrus) fruit results in the formation of stone cells, which affects the texture and quality of the fruit. However, it is still unclear that how different transcription factors (TFs) work together to coordinate the synthesis and deposition of lignin. Here, we examined the transcriptome of pear varieties with different stone cell contents and found a key TF (PbAGL7) that can promote the increase of stone cell contents and secondary cell wall thicknesses. In addition, PbAGL7 can facilitate the expression level of lignin biosynthesis-related genes and accelerate the lignin biosynthesis in pear fruit and Arabidopsis. However, PbAGL7 did not directly bind to the promoters of PbC3H1 and PbHCT17 which are crucial genes involved in lignin biosynthesis. On the other hand, yeast two-hybrid (Y2H) library showed that PbNAC47 and PbMYB73 interacted with PbAGL7 in the nucleus. PbNAC47 and PbMYB73 also increased the stone cell and lignin contents, and upregulated the expressions of PbC3H1 and PbHCT17 by binding to the SNBE and AC elements, respectively. Moreover, PbNAC47 also interacted with PbMYB73 to form PbAGL7-PbNAC47-PbMYB73 complex. This complex significantly activated the expression levels of PbC3H1 and PbHCT17 and promoted lignin biosynthesis to form stone cells in pear fruit. Overall, our study provides new insights into the molecular mechanism of TFs that coordinately regulate the stone cell formation in pear fruit and extend our knowledge to understand cell wall lignification in plants.