Rui Zhai

Parthenocarpy can ensure fruit setting without fertilization and generate seedless fruits. PbCYP78A6 has been shown to play a role in gibberellin (GA)-induced parthenocarpy in pears. However, the transcriptional response mechanism of PbCYP78A6 to GA remains unclear. In this study, using a yeast one-hybrid assay combined with co-expression analysis, PbMYB56 was initially identified as a transcription regulator of PbCYP78A6, which was further confirmed by electrophoretic mobility shift assay (EMSA) and dual-luciferase reporter assays. The biofunction of PbMYB56 was further verified using transient transgene tests, stable transgenic pear callus and tomato. PbMYB56 overexpression resulted in reduced cell death and higher fluorescence intensity after fluoresce diacetate (FDA) staining, as well as delayed fruit-drop by increasing PbCYP78A6 expression in unpollinated pear fruitlets and callus. In contrast, silencing PbMYB56 caused cell death and early fruit-drop with decreased PbCYP78A6 expression. Moreover, after emasculation, heterologous overexpression of PbMYB56 induced parthenocarpy and enlarged seed size in pollinated tomato fruits. Silencing SlMYB56, a homolog of PbMYB56 in tomatoes, resulted in smaller fruit and seed size, and these traits were restored by co-overexpression with PbCYP78A6. Furthermore, we investigated the protein interaction between PbMYB56 and PbDELLA, which is crucial component of the GA signaling pathway. This interaction inhibited PbMYB56-induced transcriptional activation of PbCYP78A6. Co-overexpression of PbMYB56 and PbDELLA contributed to reduced seed development and loss of parthenocarpy potential in tomatoes. Collectively, our study identifies PbDELLA-PbMYB56-PbCYP78A6 as a regulatory module of GA4 + 7-induced pseudo-embryo and parthenocarpy development, offering insights into the mechanism underlying parthenocarpy formation in pears.

Scientific evaluation of pear maturity is important for commercial reasons. Near-infrared spectroscopy is a non-destructive method that could be used for rapid assessment of pear maturity. The aim of this study was to develop a reasonable and effective method for the assessment of Starkrimson pear maturity using near-infrared technology. Partial least squares regression and five classification methods were used for analysis of the data. Among the indices used with the competitive adaptive reweighting–partial least squares regression method for quantitation, the visual ripeness index had the best modeling effect (Rp2: 0.87; root mean square error of prediction: 0.39). The classification model constructed with the visual ripeness index and post-ripeness score gave a cross-validation neural network model with the best classification effect and the highest accuracy (classification accuracy: 88.7%). The results showed that combination of quality indices with near-infrared spectroscopy was effective for rapidly evaluating the maturity of Starkrimson pears.

‘Yunnan’ quince (Cydonia oblonga Mill.) is used as the dwarfing rootstock for pear (Pyrus spp.). Here, we reported that the sugar contents in mature ‘Zaosu’ pear fruit grafted on ‘Yunan’ quince (Z/Q) were higher than that in ‘Zaosu’ pear fruit grafted on ‘Duli’ (Pyrus betulifolia) (Z/D). To investigate the underlying mechanism, the leaf photosynthetic capacity and the leaf-to-fruit assimilate transport capacity were initially analyzed. The leaf photosynthetic capacity was similar between Z/Q and Z/D, but the assimilate transport capacity was greater for Z/Q than for Z/D. Sugar transporters mediate the distribution of assimilates; therefore, changes in PbSWEET transcriptional patterns were examined. PbSWEET6 was highly expressed in Z/Q fruit. Thus, the PbSWEET6 function related to assimilate transport was further verified. Sucrose and glucose contents increased in transgenic tomato fruit and pear fruit calli overexpressing PbSWEET6. Taken together, these results suggest that ‘Yunnan’ quince positively regulated fruit sugar contents by influencing the flow of PbSWEET6-involved assimilates in the scion.

Fourier transform near-infrared (FT-NIR) spectroscopy is a nondestructive, rapid, real-time analysis of technical detection methods with an important reference value for producers and consumers. In this study, the feasibility of using FT-NIR spectroscopy for the rapid quantitative analysis and qualitative analysis of ‘Zaosu’ and ‘Dangshansuli’ pears is explored. The quantitative model was established by partial least squares (PLS) regression combined with cross-validation based on the spectral data of 340 pear fresh fruits and synchronized with the reference values determined by conventional assays. Furthermore, NIR spectroscopy combined with cluster analysis was used to identify varieties of ‘Zaosu’ and ‘Dangshansuli’. As a result, the model developed using FT-NIR spectroscopy gave the best results for the prediction models of soluble solid content (SSC) and titratable acidity (TA) of ‘Dangshansuli’ (residual prediction deviation, RPD: 3.272 and 2.239), which were better than those developed for ‘Zaosu’ SSC and TA modeling (RPD: 1.407 and 1.471). The results also showed that the variety identification of ‘Zaosu’ and ‘Dangshansuli’ could be carried out based on FT-NIR spectroscopy, and the discrimination accuracy was 100%. Overall, FT-NIR spectroscopy is a good tool for rapid and nondestructive analysis of the internal quality and variety identification of fresh pears.

Background: Decrease in anthocyanin content results in the loss of red color in leaves, petals and receptacles during development. The content of anthocyanin was affected by the biosynthesis and degradation of anthocyanin. Compared with the known detailed mechanism of anthocyanin biosynthesis, the degradation mechanism is not fully investigated. It is vital to study the degradation mechanism of anthocyanin in pear for promoting the accumulation of anthocyanin and inhibiting the red fading in pear. Results: Here, we reported that laccase encoded by PbLAC4-like was associated with anthocyanin degradation in pear. The expression pattern of PbLAC4-like was negatively correlated with the content of anthocyanin during the color fading process of pear leaves, petals and receptacles. Phylogenetic analysis and sequence alignment revealed that PbLAC4-like played a vital role in anthocyanin degradation. Thus, the degradation of anthocyanin induced by PbLAC4-like was further verified by transient assays and prokaryotic expression. More than 80% of anthocyanin compounds were degraded by transiently over-expressed PbLAC4-like in pear fruitlet peel. The activity of crude enzyme to degrade anthocyanin in leaves at different stages was basically consistent with the expression of PbLAC4-like. The anthocyanin degradation ability of prokaryotic induced PbLAC4-like protein was also verified by enzyme activity assay. Besides, we also identified PbMYB26 as a positive regulator of PbLAC4-like. Yeast one-hybrid and dual luciferase assay results showed that PbMYB26 activated PbLAC4-like expression by directly binding to the PbLAC4-like promoter. Conclusions: Taken together, the PbLAC4-like activated by PbMYB26, was involved in the degradation of anthocyanin, resulting in the redness fading in different pear tissues.