Transcription factor PbMYB80 regulates lignification of stone cells and undergoes RING finger protein PbRHY1-mediated degradation in pear fruit.

The Chinese white pear (Pyrus bretschneideri) fruit carries a high proportion of stone cells, adversely affecting fruit quality. Lignin is a main component of stone cells in pear fruit. In this study, we discovered that a pear MYB transcription factor, PbMYB80, binds to the promoters of key lignin biosynthesis genes and inhibits their expression. Stable overexpression of PbMYB80 in Arabidopsis showed that lignin deposition and secondary wall thickening were inhibited, and the expression of the lignin biosynthesis genes in transgenic Arabidopsis was decreased. Transient overexpression of PbMYB80 in pear fruit inhibited lignin metabolism and stone cell development, and the expression of some genes in the lignin metabolism pathway was reduced. In contrast, silencing PbMYB80 with VIGS increased the lignin and stone cell content in pear fruit, and increased expression of genes in the lignin metabolism pathway. By screening a pear fruit cDNA library in yeast, we found that PbMYB80 binds to a RING finger (PbRHY1) protein. We also showed that PbRHY1 exhibits E3 ubiquitin ligase activity and degrades ubiquitinated PbMYB80 in vivo and in vitro. This investigation contributes to a better understanding of the regulation of lignin biosynthesis in pear fruit, and provides a theoretical foundation for increasing pear fruit quality at the molecular level.

Comparative genomic analysis of the COBRA genes in six Rosaceae species and expression analysis in Chinese white pear (Pyrus bretschneideri).

COBRA-Like (COBL) genes encode a glycosylphosphatidylinositol (GPI) anchoring protein unique to plants. In current study, 87 COBRA genes were identified in 6 Rosaceae species, including Pyrus bretschneideri (16 genes), Malus domestica (22 genes), Fragaria vesca (13 genes), Prunus mume (11 genes), Rubus occidentalis (13 genes) and Prunus avium (12 genes). We revealed the evolution of the COBRA gene in six Rosaceae species by phylogeny, gene structure, conservative sequence, hydrophobicity analysis, gene replication events and sliding window analysis. In addition, based on the analysis of expression patterns in pear fruit combined with bioinformatics, we identified PbCOBL12 and PbCOBL13 as potential genes regulating secondary cell wall (SCW) formation during pear stone cell development. This study aimed to understand the evolutionary relationship of the COBRA gene in Rosaceae species, clarify the potential function of COBRA in pear fruit development, and provide essential theoretical basis and gene resources for improving pear fruit quality through genetical modification mechanism.

Comparative Genomic Analysis of TCP Genes in Six Rosaceae Species and Expression Pattern Analysis in Pyrus bretschneideri.

TCP is a plant-specific transcription factor that plays an important role in flowering, leaf development and other physiological processes. In this study, we identified a total of 155 TCP genes: 34 in Pyrus bretschneideri, 19 in Fragaria vesca, 52 in Malus domestica, 19 in Prunus mume, 17 in Rubus occidentalis and 14 in Prunus avium. The evolutionary relationship of the TCP gene family was examined by constructing a phylogenetic tree, tracking gene duplication events, performing a sliding window analysis. The expression profile analysis and qRT-PCR results of different tissues showed that PbTCP10 were highly expressed in the flowers. These results indicated that PbTCP10 might participated in flowering induction in pear. Expression pattern analysis of different developmental stages showed that PbTCP14 and PbTCP15 were similar to the accumulation pattern of fruit lignin and the stone cell content. These two genes might participate in the thickening of the secondary wall during the formation of stone cells in pear. Subcellular localization showed that PbTCPs worked in the nucleus. This study explored the evolution of TCP genes in six Rosaceae species, and the expression pattern of TCP genes in different tissues of "Dangshan Su" pear. Candidate genes related to flower induction and stone cell formation were identified. In summary, our research provided an important theoretical basis for improving pear fruit quality and increasing fruit yield by molecular breeding.