The Variation of Stone Cell Content in 236 Germplasms of Sand Pear (Pyrus pyrifolia) and Identification of Related Candidate Genes

Stone cells have been described to substantially influence pear fruit quality, as lignin and cellulose are the main components of stone cells. However, there are limited studies on the relationship between the variation and molecular basis of stone cells, lignin and cellulose content among different pear varieties. Here, to reveal the variation of stone cell content within different cultivated species, we collected 236 germplasms of sand pear (Pyrus pyrifolia) at 50 days after flower blooming (DAFB), the key stage of stone cell formation. In our results, we measured the content of stone cells, lignin and cellulose and found that these contents ranged from 2.82% to 29.00%, 8.84% to 55.30% and 11.52% to 30.55%, respectively. Further analysis showed that the variation coefficient of stone cell, lignin and cellulose content was 39.10%, 28.03% and 16.71%, respectively. Additionally, a significant correlation between stone cell, lignin and cellulose content were detected, and the correlation coefficient between the contents of stone cell and lignin (0.912) was higher than between the contents of stone cell and cellulose (0.796). Moreover, the average lignin content (29.73%) was higher than the average cellulose content (18.03%) in stone cells in pear fruits, indicating that lignin is the main component of stone cell in pears. Finally, on the basic of the transcriptome data, we identified 10 transcription factors belonging to bHLH, ERF, MYB, and NAC transcript families, which might be involved in lignin formation in stone cells. qRT-PCR experiments verified coincident trends between expression of candidate genes and stone cell content. This research laid foundation for future studies on genetic variation of stone cells in pear fruits and provided important gene resources for stone cell regulation.