Sugar metabolism reprogramming in a non-climacteric bud mutant of a climacteric plum fruit during development on the tree.

We investigated sugar metabolism in leaves and fruits of two Japanese plum (Prunus salicina Lindl.) cultivars, the climacteric Santa Rosa and its bud sport mutant the non-climacteric Sweet Miriam, during development on the tree. We previously characterized differences between the two cultivars. Here, we identified key sugar metabolic pathways. Pearson coefficient correlations of metabolomics and transcriptomic data and weighted gene co-expression network analysis (WGCNA) of RNA sequencing (RNA-Seq) data allowed the identification of 11 key sugar metabolism-associated genes: sucrose synthase, sucrose phosphate synthase, cytosolic invertase, vacuolar invertase, invertase inhibitor, α-galactosidase, ß-galactosidase, galactokinase, trehalase, galactinol synthase, and raffinose synthase. These pathways were further assessed and validated through the biochemical characterization of the gene products and with metabolite analysis. Our results demonstrated the reprogramming of sugar metabolism in both leaves and fruits in the non-climacteric plum, which displayed a shift towards increased sorbitol synthesis. Climacteric and non-climacteric fruits showed differences in their UDP-galactose metabolism towards the production of galactose and raffinose, respectively. The higher content of galactinol, myo-inositol, raffinose, and trehalose in the non-climacteric fruits could improve the ability of the fruits to cope with the oxidative processes associated with fruit ripening. Overall, our results support a relationship between sugar metabolism, ethylene, and ripening behavior.

Comparative RNA-Seq profiling of berry development between table grape 'Kyoho' and its early-ripening mutant 'Fengzao'.

BACKGROUND: Early ripening is an important desirable attribute for fruit crops. 'Kyoho' is a popular table grape cultivar in many Asian countries. 'Fengzao' is a bud mutant of 'Kyoho' and ripens nearly 30 days earlier than 'Kyoho'. To identify genes controlling early fruit development and ripening in 'Fengzao', RNA-Seq profiles of the two cultivars were compared at 8 different berry developmental stages in both berry peel and flesh tissues. METHODS: RNA-Seq profiling of berry development between 'Kyoho' and 'Fenzhao' were obtained using the Illumina HiSeq system and analyzed using various statistical methods. Expression patterns of several selected genes were validated using qRT-PCR. RESULTS: About 447 millions of RNA-Seq sequences were generated from 40 RNA libraries covering various different berry developmental stages of 'Fengzao' and 'Kyoho'. These sequences were mapped to 23,178 and 22,982 genes in the flesh and peel tissues, respectively. While most genes in 'Fengzao' and 'Kyoho' shared similar expression patterns over different berry developmental stages, there were many genes whose expression were detected only in 'Fengzao' or 'Kyoho'. We observed 10 genes in flesh tissue and 22 genes in peel tissue were differentially expressed at FDR ≤ 0.05 when the mean expression of 'Fengzao' and 'Kyoho' were compared. The most noticeable one was VIT_214s0030g00950 (a superoxide dismutase gene). This ROS related gene showed lower expression levels in 'Fengzao' than 'Kyoho' in both peel and flesh tissues across various berry developmental stages with the only exception at véraison. VIT_200s0238g00060 (TMV resistance protein n-like) and VIT_213s0067g01100 (disease resistance protein at3g14460-like) were the two other noticeable genes which were found differentially expressed between the two cultivars in both peel and flesh tissues. GO functional category and KEGG enrichment analysis of DEGs indicated that gene activities related to stress and ROS were altered between the two cultivars in both flesh and peel tissues. Several differentially expressed genes of interest were successfully validated using qRT-PCR. CONCLUSIONS: Comparative profiling analysis revealed a few dozens of genes which were differentially expressed in the developing berries of 'Kyoho' and its early ripening mutant 'Fengzao'. Further analysis of these differentially expressed genes suggested that gene activities related to ROS and pathogenesis were likely involved in contributing to the early ripening in 'Fengzao'.

Volatile metabolomics and transcriptomics analyses provide insights into the mechanism of volatile changes during fruit development of 'Ehime 38' (Citrus reticulata) and its bud mutant.

Volatile compounds are important determinants affecting fruit flavor. Previous study has identified a bud mutant of 'Ehime 38' (Citrus reticulata) with different volatile profile. However, the volatile changes between WT and MT during fruit development and underlying mechanism remain elusive. In this study, a total of 35 volatile compounds were identified in the pulps of WT and MT at five developmental stages. Both varieties accumulated similar and the highest levels of volatiles at stage S1, and showed a downward trend as the fruit develops. However, the total volatile contents in the pulps of MT were 1.4-2.5 folds higher than those in WT at stages S2-S5, which was mainly due to the increase in the content of d-limonene. Transcriptomic and RT-qPCR analysis revealed that most genes in MEP pathway were positively correlated with the volatile contents, of which DXS1 might mainly contribute to the elevated volatiles accumulation in MT by increasing the flux into the MEP pathway. Moreover, temporal expression analysis indicated that these MEP pathway genes functioned at different developmental stages. This study provided comprehensive volatile metabolomics and transcriptomics characterizations of a citrus mutant during fruit development, which is valuable for fruit flavor improvement in citrus.

Comparison of reactive oxygen species metabolism during grape berry development between 'Kyoho' and its early ripening bud mutant 'Fengzao'.

Enzymes and non-enzyme elements related to the metabolism of reactive oxygen species (ROS), such as catalase (CAT), superoxide dismutase (SOD), ascorbic acid (AsA), glutathione (GSH), NADPH oxidase (NOX), hydrogen peroxide (H2O2), superoxide anion (O2-), lipoxygenase (LOX) and malondialdehyde (MDA), were measured in 'Kyoho' and its early ripening bud mutant 'Fengzao' to compare ROS level changes and investigate the potential roles of ROS in grape berry development and the ripening process. In addition, the anthocyanin and sugar contents as well as berry diameter were also investigated at different berry development stages. The results showed that the H2O2 content and LOX activity exhibited obviously different trends between 'Fengzao' and 'Kyoho' during the berry development stages. Before berry softening, the SOD activity, LOX activity and H2O2 content were significant lower in 'Fengzao' than in 'Kyoho', but there were no significant differences in the production rate of O2-, ROS scavengers (CAT, AsA, GSH) and MDA content between them, which indicated that the higher oxidation status in 'Fengzao'. It may promote the faster development of 'Fengzao' berry than 'Kyoho' before berry softening (EL31-33). The significant higher LOX and CAT activities at EL-34, as well as significant higher LOX activity and H2O2 content at EL-35 in 'Fengzao' than in 'Kyoho' indicated H2O2 was acted as the appropriate oxidative stress factor and the signal molecule to further accelerate the berry ripening of 'Fengzao'. The increasing O2- and H2O2 after EL-35 in 'Fengzao' further promoted the ripening process. Furthermore, after the spraying of 300 µmol/L H2O2 solution on 'Kyoho' at EL-31 stage, the berries matured 15 days earlier than the untreated. Evidence in this study indicated that the overall oxidation status (ROS levels) in 'Fengzao' is higher than in 'Kyoho' and H2O2 could promote the early ripening of 'Kyoho' berry.