Huanglongbing (HLB, previously known as citrus greening), is associated with Candidatus Liberibacter species and is a serious threat to citrus production world-wide. The pathogen is a Gram negative, unculturable, phloem-limited bacterium with limited known genomic information. Expanding the genetic knowledge of this organism may provide better understanding of the pathogen and possibly develop effective strategies for control and management of HLB.

The establishment and application of a two-crop-a-year cultivation system depends on the particularity of climatic conditions in subtropical regions. The different temperature, light, and water conditions throughout the growing season of summer and winter grapes are the fundamental reasons for differences in primary and secondary metabolites. We performed ultra-high-performance liquid chromatography–triple quadrupole mass spectrometry (UPLC-QQQ-MS)-based metabolomics on ‘Kyoho’ grapes under a two-crop-a-year cultivation system. In total, 1062 metabolites were identified and classified into 10 different categories, while flavonoids were the largest group, with 285 metabolites. Moreover, 876 metabolites were different among the four developmental stages, and 551 were different between the summer and winter grapes during the same growth period. Hierarchical clustering analysis (HCA) and principal component analysis (PCA) clearly distinguished developmental and growth-season differences based on the detected metabolites. Of note, flavonoids were the most important compounds responsible for the differences in berry composition during the growth and developmental seasons. The content of most flavonoids was higher in the winter grapes, but some were also found at higher levels in summer grapes, such as kaempferol-4′-O-glucoside, leucocyanidin, and cyanidin-3-O-glucosylglucoside. Additionally, myricetin-3-O-arabinoside was consistently higher in winter grapes than in summer grapes during all four developmental stages. The extreme high temperature and higher relative humidity were important reasons for the lower flavonoid content in the summer grapes than in the winter grapes. Moreover, the stronger light intensity in the early development of the winter grapes had a positive effect on the accumulation of flavonoids, especially flavonols and flavan-3-ols. This study provides new insights into the metabolism of flavonoids in grapes under a two-crop-a-year cultivation system and explores the climatic causes of the differences in the metabolites in the two crops of grapes.

Grapevine is a popular cultivated fruit throughout the world and heat stress is one of the most serious threats to viticulture. However, transcriptional responses, such as molecular properties of photosynthesis and abscisic acid biosynthesis, metabolism and signal transduction pathway of grapevine to heat stress, are still poorly understood. In this study, RNA-seq was carried out for thermostabilized grapevine ‘Kyoho’ leaves. Results showed that 685 and 469 genes were commonly down-regulated and up-regulated at three sampling time-points. The light-dependent reactions of photosynthesis was significantly enriched in up-regulated DEGs at 1 hpt and down-regulated DEGs at R24 hpt. Heat stress impaired the photosynthetic capacity of grapevine leaves, and there was a significant positive relationship between photosynthesis and stomatal conductance at short-term post-heat stress treatment, but the inhibition of HS on Pn was non-stomata limitation for a longer period. Photosystem (PS)Ⅱ was more sensitive to heat stress than PSⅠ, and PsbP, as well as Psb28, played important roles in response to heat stress. The abscisic acid (ABA) content in heat-stress-treated Kyoho plants was higher than that in the control at 1 hpt, but less in heat-stress-treated plants at 4 and R24 hpt, which was regulated by numerous genes involved in the ABA biosynthesis and catabolism pathways. These results help to understand the influence of heat stress on photosynthesis and ABA biosynthesis, metabolism and signal transduction pathway.

Under the double cropping system, berries usually showed significant quality variations in the summer and winter seasons. In the two-year/four-consecutive-season study, two table grapes of ‘Muscat Hamburg’ and ‘Victoria’ were investigated to determine the phenolic compounds in their berries. Different from those of the summer season, the berries in the winter season suffered no high-temperature stress since veraison to harvest in 2014 and 2015. The variations in the season temperatures led to a higher anthocyanin concentration in the winter season berries of ‘Muscat Hamburg’ grapes than that in the summer berries, while the summer season berries had higher proportions of acylated and methylated anthocyanins than those in the winter season berries. Similar to the anthocyanins, the winter season berries also had a higher flavonol concentration in both varieties. Transcriptome analysis showed that the upregulated genes involved in the flavonoid pathway in the winter season berries were agreed with the changes found in the metabolites. However, the influence of the growing seasons on the flavanols was not consistent in the two varieties, and the variations in VviLARs between the grapes of ‘Muscat Hamburg’ and ‘Victoria’ might be the cause. This research helped us better understand the double cropping system and how the climate factors affected the phenolic compounds in the double cropping system.

Background: The global transcriptome reprogramming in grapevines in response to powdery mildew remains poorly understood, despite its economic implications, especially the new cultivars. Methods: Thus, this study aimed to elucidate these changes through RNA sequencing in ‘Yeniang No. 2’ grapevine leaves infected with powdery mildew compared to healthy ones. Results: A total of six samples were subjected to transcriptome sequencing, resulting in 36.85 Gb of clean data. A minimum of 5.89 Gb of clean data was generated for each sample, with at least 92.24% of the clean data attaining a quality score of Q30. Clean reads from each sample were aligned to the designated reference genome. The mapping ratio varied between 88.77% and 89.66%. The high-quality sequencing data revealed 1219 differentially expressed genes (DEGs), of which the infection upregulated 790 and downregulated 429. Functional enrichment analyses revealed a significant activation of key defense-related pathways. These included plant–pathogen interaction, phenylpropanoid and flavonoid biosynthesis for creating antimicrobial compounds, glutathione metabolism for reducing oxidative stress, and oxidative phosphorylation for enhanced energy production. This indicates a coordinated, multi-faceted defense strategy. The study also uncovered a complex layer of post-transcriptional regulation, identifying 1883 novel genes and 22,210 alternative splicing events, primarily skipped exons and intron retention. Key hub proteins identified within interaction networks, along with these splicing changes, underscore a sophisticated defense involving transcriptional reprogramming and metabolic shifts. Conclusions: The genes and molecular markers discovered are valuable resources for marker-assisted breeding. Leveraging these findings, particularly hub genes and favorable splice variants, can accelerate the development of new grapevine cultivars with durable resistance to powdery mildew.