First purchases of fruit are mainly dependent on aspects of appearance such as color. However, repeat buys of fruit are determined by internal quality traits such as flavor-related volatiles. Differences in volatile profiles in white- and red-fleshed peach fruit are not well understood. In the present study, peach cultivars with white- and red-fleshed fruit were subjected to sensory analysis using electronic nose (e-nose) to evaluate overview volatile profiles. Approximately 97.3% of the total variation in peach color-volatiles was explained by the first principle component 1 (PC1) and PC2. After analyzing sensory differences between peach fruit samples, 50 volatile compounds were characterized based on GC-MS. Multivariate analysis such as partial least squares discriminant analysis (PLS-DA) was applied to identify volatile compounds that contribute to difference in white- and red-fleshed peach fruit cultivars. A total of 18 volatiles that could separate peach fruit cultivars with different colors in flesh during ripening were identified based on variable importance in projection (VIP) score. Fruity note latone γ-hexalactone had higher contents in red-fleshed cultivars, while grassy note C6 compounds such as hexanal, 2-hexenal, (E)-2-hexenal, 1-hexanol, and (Z)-2-hexen-1-ol showed great accumulation in white-fleshed peach fruit.

Calmodulin-binding transcription activator (CAMTA) is a transcription factor family containing calmodulin (CaM) binding sites and is involved in plant development. Although CAMTAs in Arabidopsis have been extensively investigated, the functions of CAMTAs remain largely unclear in peaches. In this study, we identified five peach CAMTAs which contained conserved CG-1 box, ANK repeats, CaM binding domain (CaMBD) and IQ motifs. Overexpression in tobacco showed that PpCAMTA1/2/3 were located in the nucleus, while PpCAMTA4 and PpCAMTA5 were located in the plasma membrane. Increased expression levels were observed for PpCAMTA1 and PpCAMTA3 during peach fruit ripening. Expression of PpCAMTA1 was induced by cold treatment and was inhibited by ultraviolet B irradiation (UV-B). Driven by AtCAMTA3 promoter, PpCAMTA1/2/3 were overexpressed in Arabidopsis mutant. Here, we characterized peach PpCAMTA1, representing an ortholog of AtCAMTA3. PpCAMTA1 expression in Arabidopsis complements the developmental deficiencies of the camta2,3 mutant, and restored the plant size to the wild type level. Moreover, overexpressing PpCAMTA1 in camta2,3 mutant inhibited salicylic acid (SA) biosynthesis and expression of SA-related genes, resulting in a susceptibility phenotype to Pst DC3000. Taken together, our results provide new insights for CAMTAs in peach fruit and indicate that PpCAMTA1 is associated with response to stresses during development.

Background: The established genetic transformation system is essential for gene function research and genetic improvement of horticultural crops. The lack of efficient genetic transformation systems has long been a significant bottleneck for perennial fruit trees such as peach. Results: In this study, we provided an Agrobacterium rhizogenes -mediated transformation system by using stem segments of the ‘Hanlumi’ cultivar ( Prunus persica L. Batsch). Through the optimization of explants, selection of the appropriate bacterial strain (MSU440), and determination of the infection concentration (OD ₆₀₀ = 1.0), we obtained transgenic callus and hairy roots with stable GFP expression. Additionally, a rapid transient transformation system was also developed using callus derived from stem and fruit tissues. Both systems were applied to functionally characterize genes involved in the biosynthesis of flavor-related C6 aldehydes. Overexpression of PpLOX1 or PpHPL1 in transgenic callus led to a significant increase in the levels of hexanal and E -2-hexenal, whereas RNAi silencing of PpLOX6 or PpHPL1 in callus resulted in a marked decrease. These results demonstrate that PpLOX1 , PpLOX6 , and PpHPL1 are key genes in the peach C6 aldehyde pathway. Conclusions: The established transformation systems provide effective means for gene function validation and molecular breeding in peach, which have significant implications for the improvement of flavor quality.