Abstract
Fruit hardening, one of the physiological disorders influencing the quality of pear, is usually accompanied by fruit lignification. Nonetheless, the mechanism by which lignin accumulates in hardened pear fruit is still unknown. Here, Transcriptome analysis of normal fruits (NFs) and hardened fruits (HFs) of ‘Suli’ pear (Pyrus bretschneideri Rehd) was used to examine the molecular mechanism of fruit hardening. We found that hardened fruits (HFs), especially those in the top region within 35–180 days after flowering (DAF), possessed a prominently higher lignin level than normal fruits (NFs). Subsequently, transcriptome sequencing of fruit at 35 DAF identified 4391 [HF shoulder region (HF_S) vs. NF top region (NF_T)], 3849 (HF_T vs. NF_T) and 408 (HF_T vs. HF_S) differentially expressed genes. Among them, we clarified 26 unigenes that encode 10 enzymes as candidate genes participating in lignin biosynthesis. Thus, high expression of the lignin biosynthetic gene impels lignin to accumulate in HFs. Some transcription factors were evaluated to link with lignin formation and subsequently analysed. In addition, the genes participating in flavonoid/proanthocyanidin biosynthesis dropped from the HF_T to the HF_S, suggesting that the flavonoid metabolic pathway was reduced to promote intermediate metabolites to be converted to the lignin biosynthetic pathway. To conclude, this study lays a solid theoretical foundation and provides reference data for investigating the mechanism by which lignin accumulates in hardened pear fruit.
Highlights
Fruit hardening, one of the physiological disorders influencing the quality of pear, is usually accompanied by fruit lignification
Fleshy tissues were chosen from the top region of normal fruits (NFs) (NF_T), the shoulder region of hardened fruits (HFs) (HF_S) and the top region of HFs (HF_T) at 35 DAP for the transcriptomic analysis, so as to determine factors controlling lignin biosynthesis in the early phase
The results revealed that there was an apparent protrusion in the HF_T (Figure 1A)
Summary
One of the physiological disorders influencing the quality of pear, is usually accompanied by fruit lignification. The mechanism by which lignin accumulates in hardened pear fruit is still unknown. Transcriptome analysis of normal fruits (NFs) and hardened fruits (HFs) of ‘Suli’ pear (Pyrus bretschneideri Rehd) was used to examine the molecular mechanism of fruit hardening. We found that hardened fruits (HFs), especially those in the top region within 35–180 days after flowering (DAF), possessed a prominently higher lignin level than normal fruits (NFs). ‘Suli’ pear (Pyrus bretschneideri Rehd), has long been cultivated in a broad geographical area in China [1]. This variety in Shanxi Province of China has shown severe fruit hardening in recent years. Researchers speculate that texture hardening in pear fruit is attributable to scion-rootstock compatibility problems, which causes physiological imbalance, such as water stress and calcium deficiency [6,7,8]
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