Effects of Metaxenia on Stone Cell Formation in Pear (Pyrus bretschneideri) Based on Transcriptomic Analysis and Functional Characterization of the Lignin-Related Gene PbC4H2

Xi Cheng,Han Wang,Guohui Li,Chongchong Yan,Qing Jin,Yi Lin,Jinyun Zhang,Yongping Cai,Tianzhe Chen

doi:10.3390/f11010053

Xi Cheng, Han Wang + Show 7 more

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https://doi.org/10.3390/f11010053

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Abstract

The deposition of lignin in flesh parenchyma cells for pear stone cells, and excessive stone cells reduce the taste and quality of the fruit. The effect of metaxenia on the quality of fruit has been heavily studied, but the effect of metaxenia on stone cell formation has not been fully elucidated to date. This study used P. bretschneideri (Chinese white pear) cv. ‘Yali’ (high-stone cell content) and P. pyrifolia (Sand pear) cv. ‘Cuiguan’ (low-stone cell content) as pollination trees to pollinate P. bretschneideri cv. ‘Lianglizaosu’ separately to fill this gap in the literature. The results of quantitative determination, histochemical staining and electron microscopy indicated that the content of stone cells and lignin in YL fruit (‘Yali’ (pollen parent) × ‘Lianglizaosu’ (seed parent)) was significantly higher than that in CL fruit (‘Cuiguan’ (pollen parent) × ‘Lianglizaosu’ (seed parent)). The transcriptome sequencing results that were obtained from the three developmental stages of the two types of hybrid fruits indicated that a large number of differentially expressed genes (DEGs) related to auxin signal transduction (AUX/IAAs and ARFs), lignin biosynthesis, and lignin metabolism regulation (MYBs, LIMs, and KNOXs) between the CL and YL fruits at the early stage of fruit development. Therefore, metaxenia might change the signal transduction process of auxin in pear fruit, thereby regulating the expression of transcription factors (TFs) related to lignin metabolism, and ultimately affecting lignin deposition and stone cell development. In addition, we performed functional verification of a differentially expressed gene, PbC4H2 (cinnamate 4-hydroxylase). Heterologous expression of PbC4H2 in the c4h mutant not only restored its collapsed cell wall, but also significantly increased the lignin content in the inflorescence stem. The results of our research help to elucidate the metaxenia-mediated regulation of pear stone cell development and clarify the function of PbC4H2 in cell wall development and lignin synthesis, which establishes a foundation for subsequent molecular breeding.

Highlights

Pear (Pyrus spp.) is one of the world’s most important Rosaceae deciduous trees, but it is the third most abundant fruit in China [1]
We found that the AcBr lignin content in the inflorescence stem of the c4h mutant was reduced approximately 24% s compared with that of the WT plants, and the difference reached a significant by approximately 24% s compared with that of the WT plants, and the difference reached a level, through the detection of acetyl bromide (AcBr) lignin (Figure 11a)
(pollen parent) × ‘Lianglizaosu’ as the materials to demonstrate that metaxenia can significantly affect stone cell development and lignin metabolism in pear fruit

Summary

Introduction

Pear (Pyrus spp.) is one of the world’s most important Rosaceae deciduous trees, but it is the third most abundant fruit in China [1]. Asian pears are mainly grown in Asia, including P. bretschneideri, P. pyrifolia, P. sinkiangensis (Xinjiang pear), and P. ussuriensis (Ussurian pear) [2]. ‘Dangshan Su’), which belongs to Chinese white pear (P. bretschneideri), is the most abundant pear variety that is cultivated in China and it is one of the main exported varieties. The large diameter of stone cell clusters in the fruit of this variety is excessive, which causes a gritty texture and coarse taste [3,4,5]

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