<i>VcLOB107</i> acts as an important regulator of fruit firmness differences between firm and soft flesh blueberries

Fruit firmness is a significant trait for blueberry breeding as it affects machinery harvest, consumer preference, and transportability. LOB transcription factors play a vital role in the development of lateral organs and growth in higher plants; yet, few studies on LOB transcription factors have been reported in blueberries. We performed a genome-wide identification analysis of the blueberry <italic>LOB</italic> gene family. Using fruit at different developmental stages from the firm-flesh cultivar 'Star', and the soft-flesh cultivar 'O'Neal', the fruit firmness, polygalacturonase (PG) activity, and pectin content of different types were detected. A total of 150 <italic>VcLOB</italic> genes were identified in the blueberry genome, unevenly distributed across 46 chromosomes. They could be divided into six subfamilies, with members in each subfamily sharing similar gene structures and motifs. Based on the transcriptomic data and fruit firmness of two blueberry cultivars, four <italic>VcLOB</italic> genes functioning during the critical period of fruit firmness variation were selected, and their expression patterns were dissected, revealing differences in the expression pattern across various tissues and throughout the fruit development stages in blueberries. The fruit firmness of 'O'Neal' is significantly lower than that of 'Star' from stages S5 to S8 during fruit development. Additionally, the PG activity and water-soluble pectin content in 'O'Neal' is significantly higher than those in 'Star'. <italic>VcLOB107</italic> overexpressed tomato plants exhibited notably higher fruit firmness, lower PG activity, and WSP content compared to the control group, indicating VcLOB107 is a regulator of fruit firmness differences between firm and soft flesh blueberries.