Integration of Transcriptome and Methylome Analyses Provides Insight Into the Pathway of Floral Scent Biosynthesis in Prunus mume

DNA methylation is a common epigenetic modification involved in regulating many biological processes. However, the epigenetic mechanisms involved in the formation of floral scent have rarely been reported within a famous traditional ornamental plant Prunus mume emitting pleasant fragrance in China. By combining whole-genome bisulfite sequencing and RNA-seq, we determined the global change in DNA methylation and expression levels of genes involved in the biosynthesis of floral scent in four different flowering stages of P. mume. During flowering, the methylation status in the “CHH” sequence context (with H representing A, T, or C) in the promoter regions of genes showed the most significant change. Enrichment analysis showed that the differentially methylated genes (DMGs) were widely involved in eight pathways known to be related to floral scent biosynthesis. As the key biosynthesis pathway of the dominant volatile fragrance of P. mume, the phenylpropane biosynthesis pathway contained the most differentially expressed genes (DEGs) and DMGs. We detected 97 DMGs participated in the most biosynthetic steps of the phenylpropane biosynthesis pathway. Furthermore, among the previously identified genes encoding key enzymes in the biosynthesis of the floral scent of P. mume, 47 candidate genes showed an expression pattern matching the release of floral fragrances and 22 of them were differentially methylated during flowering. Some of these DMGs may or have already been proven to play an important role in biosynthesis of the key floral scent components of P. mume, such as PmCFAT1a/1c, PmBEAT36/37, PmPAL2, PmPAAS3, PmBAR8/9/10, and PmCNL1/3/5/6/14/17/20. In conclusion, our results for the first time revealed that DNA methylation is widely involved in the biosynthesis of floral scent and may play critical roles in regulating the floral scent biosynthesis of P. mume. This study provided insights into floral scent metabolism for molecular breeding.

Rootstock-Mediated Transcriptional Changes Associated with Cold Tolerance in Prunus mume Leaves

Japanese apricot (Prunus mume) is remarkably valuable for its high ornamental and economic importance due to its distinctive features. Low temperature is a serious environmental constraint for this species, restricting its cultivation and dispersal in the north of China. To address this issue, breeding requires an understanding of the molecular mechanisms underlying responses to cold stress. We examined the leaf physiological and transcriptome profile by RNA sequencing in ‘Bungo’ scion cultivar grafted onto Prunus mume (cold-sensitive) and Prunus armeniaca (cold-tolerant) rootstocks at 4 °C for 0, 6, and 24 h. Our results revealed that the increased MDA concentration in the leaves of P. mume cultivar (cold-sensitive) suggests that cold stress might cause oxidative damage and increased sensitivity. Moreover, the cold-tolerant cultivar (P. armeniaca) considerably enhances the enzyme activities (i.e., SOD, POD, and CAT), as well as osmo-protectants (soluble sugars and proline) compared with sensitive cultivar, which helps plants to withstand oxidative damage caused by cold stress. Additionally, differentially expressed genes were shown to be enriched in plant hormone signal transduction, ribosome, MAPK signaling, and circadian rhythm pathway. After 24 h of cold stress, genes related to PYL4, histidine kinase 1, SAUR36, bHLH130, bHLH123, TIFY 6B-like, WRKY 40, WRKY 57, and 60S acidic ribosomal protein P1 were differentially expressed, implying that these DEGs involved in multiple pathways are involved in cold tolerance in Japanese apricot. This study improved our current understanding of the mechanism of cold tolerance in Japanese apricot, and the findings could be utilized for other related fruit species.

Qualidade físico-química de ameixas ‘Letícia’ produzidas sobre porta-externos clonais e em plantas autoenraizadas, no meio-oeste de Santa Catarina

Objetivou-se com esse trabalho avaliar os efeitos de porta-enxertos clonais e de plantas autoenraizadas na qualidade físico-química de ameixas ‘Letícia’, no meio-oeste de Santa Catarina-SC. Foram avaliados frutos da cv. Letícia produzidos nos ciclos produtivos de 2018, 2019 e 2020, provenientes de pomar experimental da Estação Experimental da Epagri em Videira-SC. As plantas foram enxertadas sobre 19 diferentes acessos (cultivares, híbridos interespecíficos e seleções) utilizados como porta-enxertos clonais, além da cv. Letícia autoenraizada (sem porta-enxerto). Avaliou-se acidez total, teor de sólidos solúveis, ratio, pH, firmeza de polpa e cor da epiderme dos frutos. Os valores de pH oscilaram de 2,98 para o porta-enxerto ‘Barrier’ (2018) a 3,68 para plantas sobre ‘Santa Rosa’ (2020). ‘Santa Rosa’ como porta-enxerto destacou-se pelo maior ratio (19,46) na safra 2020, seguido pelo ‘Flordaguard em 2018 (14,92). Os maiores valores de firmeza foram obtidos para GxN9 em 2018 e Nemared em 2020, e os menores por ‘Santa Rosa’ em 2019 e 2020. A resposta dos porta-enxertos não se repetiu ao longo das safras avaliadas, demonstrando que o fator safra teve maior influência sobre a qualidade dos frutos, com exceção de ‘Santa Rosa’. Os porta-enxertos Rigitano, Clone 15 (Prunus mume), Nemared e I-67-52-4 (P. persica) apresentaram incompatibilidade com a cultivar-copa Letícia. Plantas autoenraizadas de ‘Letícia’ produzem frutos com características físico-químicas semelhantes aos produzidos em plantas enxertadas nos porta-enxertos testados, tornando-se uma opção tecnicamente interessante de cultivo sem o uso de porta-enxertos.

Headspace Volatiles and Endogenous Extracts of Prunus mume Cultivars with Different Aroma Types

Prunus mume is a traditional ornamental plant, which owed a unique floral scent. However, the diversity of the floral scent in P. mume cultivars with different aroma types was not identified. In this study, the floral scent of eight P. mume cultivars was studied using headspace solid-phase microextraction (HS-SPME) and organic solvent extraction (OSE), combined with gas chromatography-mass spectrometry (GC-MS). In total, 66 headspace volatiles and 74 endogenous extracts were putatively identified, of which phenylpropanoids/benzenoids were the main volatile organic compounds categories. As a result of GC-MS analysis, benzyl acetate (1.55–61.26%), eugenol (0.87–6.03%), benzaldehyde (5.34–46.46%), benzyl alcohol (5.13–57.13%), chavicol (0–5.46%), and cinnamyl alcohol (0–6.49%) were considered to be the main components in most varieties. However, the volatilization rate of these main components was different. Based on the variable importance in projection (VIP) values in the orthogonal partial least-squares discriminate analysis (OPLS-DA), differential components of four aroma types were identified as biomarkers, and 10 volatile and 12 endogenous biomarkers were screened out, respectively. The odor activity value (OAV) revealed that several biomarkers, including (Z)-2-hexen-1-ol, pentyl acetate, (E)-cinnamaldehyde, methyl salicylate, cinnamyl alcohol, and benzoyl cyanide, contributed greatly to the strong-scented, fresh-scented, sweet-scented, and light-scented types of P. mume cultivars. This study provided a theoretical basis for the floral scent evaluation and breeding of P. mume cultivars.