*3.8. Expression Analysis of PebHLHs*

Transcriptome analyses showed that the PebHLH genes were differentially expressed under four abiotic stresses (Figure 7). *PebHLH10/11/25/35/36/43/46/68/69/80/117* were induced by drought stress, while *PebHLH6/8/55/63/64/70/83* were suppressed. For the salt treatment, the expression of most genes was highest when treated with salt stress for 3 days. Especially, *PebHLH4* and *PebHLH56* were significantly upregulated under salt stress (NaCl 10d). However, the expression of *PebHLH8/55/63/64/70/83* was suppressed. Under hightemperature stress, some *PebHLHs* were upregulated, such as *PebHLH1/2/5/73/74/92/104*, and some genes were suppressed, such as *PebHLH8/55/63/64/70/83*. Under cold stress, the expression of the most gene had been induced, such as *PebHLH28/29/34/56/57/65/67/85/91/96/ 107/106/112*. We performed qRT-PCR validation analysis on some of the *PebHLH* genes (Figure 8). The result showed that the gene expression patterns were the same as heatmaps. The *PebHLHs* could respond to various abiotic stresses.

The expression levels of *PebHLHs* were obtained based on transcriptional sequencing results [51] at three different fruit ripening stages (T1, T2, and T3) (Figure 9). Most genes had the highest expression levels in the first period (T1) and regularly decreased in T2 and T3. And the expression of some genes was highest in T2, such as *PebHLH5/6/28/34/41/42/65/68/81/* 91/95/100/105/106/107. A few reached the maximum expression in T3, such as *PebHLH13/ 17/52/62/69/73/74/76/85/101/103/104/109*. This result indicated that the expression of most *PebHLH* genes was negatively correlated with fruit ripening. Some genes were chosen to do the qRT-PCR verification (Figure 10), which showed that the expression trends of *PebHLHs* were consistent with the transcriptome.
