Comparative evaluation of physiological and molecular responses of blackcurrant varieties to powdery mildew infection

Abstract

The black currant (Ribes nigrum L.), a member of the Saxifragaceae family's Ribes genus, has gained consumer and grower acceptance due to its high nutritional value and economic potential. However, powdery mildew, the primary leaf disease affecting black currants, significantly impacts growers and the industry. Developing varieties highly resistant to powdery mildew is currently considered the most scientifically sound solution. However, the black currant's physiological and disease resistance mechanisms post-infection by powdery mildew remain understudied, thereby impeding further breeding efforts. Therefore, this study aimed to elucidate the pathogenesis of powdery mildew in various susceptible varieties, post-infection physiological changes, and molecular mechanisms related to powdery mildew. This was achieved through phenotypic observation, physiological data analysis, transcriptomic analysis, and qRT-PCR-mediated gene expression analysis.

Keywords: blackcurrant; endogenous hormone; powdery mildew; resistance enzyme activity; transcriptome.

Figure 1

Line graphs and radar plots of changes in photosynthetic indicators. (A) Line chart of SPAD value change of susceptible varieties post-powdery mildew infection; (B1–B5). The chlorophyll fluorescence radar map of the healthy, beginning of infestation, middle infestation, flourishing infestation, and terminal of infestation periods, respectively. (C) Line chart of Fv/Fm changes after infection of susceptible varieties with powdery mildew. The average of resistant and susceptible varieties in (A, C) was calculated from five biological replicates and three technical replicates. The coordinates represent the infection period (horizontal) and its corresponding value (vertical).

Figure 2

Line and bar graphs of changes in resistance enzyme activity. The columns labelled 1, 2, and 3 in Figures 1 , 2 and 3 , respectively, represent line graphs of the mean activity of resistant and susceptible varieties, histograms of the activity of resistant varieties, and histograms of the activity of susceptible varieties. (A–E) represent the POD, CAT, PPO, PAL, and SOD activities, respectively. The horizontal and vertical coordinates indicate the infestation period and enzyme activity values, respectively.

Figure 3

Line graph of endogenous hormone changes. Change of endogenous hormone content post-powdery mildew infection. The horizontal and vertical coordinates indicate the onset period and the endogenous hormone content, respectively. (A) Changes of endogenous IAA content; (B) Changes of endogenous ABA content; (C) Changes of endogenous GA₃ content; (D) Changes of endogenous SA content.

Figure 4

Volcano, bar and bubble plots of transcriptome data. (A1, C1, D1, E1) represent LYH vs LYI group; (A2, C2, D2, E2) represents LYI vs LYM group respectively; (A3, C3, D3, E3) represents LYH vs LYM group respectively. (A1, A2, A3) The volcano indicates the DEGs. (B) The Venn diagram of LYH, LYI, LYM. (C1, C2, C3) GO analysis of DEGs classified as biological, cellular, or molecular functions. (D1, D2, D3) Analysis of DEGs classified as cellular processes, environmental information processing, metabolism and organismal systems. (E1, E2, E3) Enrichment analysis of DEGs pathway. The X and Y-axis represent enrichment factor and pathway names, respectively. A colored bubble represents q-value, and Rich Factor refers to the value of enrichment factor, which is the quotient of foreground value (the number of DEGs).

Figure 5

Diagram of the synthetic pathway shared by LYH vs LYI and LYI vs LYM. Red and green indicate up and down regulated expression, respectively, while blue indicates up-down regulated expression. (A1) Pathway map of Group LYH vs LYI Monoterpenoid biosynthetic pathway, (A2) Pathway map of Group LYI vs LYM flavonoid biosynthesis pathway. (B1) Pathway map of Group LYH vs LYI Flavonoid biosynthesis pathway, (B2) Pathway map of Group LYI vs LYM flavonoid biosynthesis pathway. (C1) Pathway map of Group LYH vs LYI Plant hormone signaling pathways, (C2) Pathway map of Group LYI vs LYM Plant hormone signaling pathways. (D1) Pathway map of Group LYH vs LYI Conversion pathway of pentose and hexuronic acid, (D2) Pathway map of Group LYI vs LYM Conversion pathway of pentose and hexuronic acid.

Figure 6

Changes in relative expression of genes associated with physiological data. The horizontal and vertical axes represents the infection duration, and the relative gene expression level, respectively. (A) Changes of POD-related gene DN7123_c0_g1 expression; (B) Changes of CAT-related gene DN8590_c0_g3 expression; (C) Changes of PAL-related gene DN2082_c0_g1 expression; (D) Changes of SOD-related gene DN64_c0_g2 expression; (E) Changes of IAA-related gene DN4946_c0_g1 expression; (F) Changes of ABA-related gene DN12960_c1_g3 expression; (G) Changes of GA₃-related gene DN14115_c1_g1 expression; (H) Changes of SA-related gene DN6918_c1_g1 expression.

Figure 7

Photographs of various periods of powdery mildew infestation of blackcurrant. (A) Beginning of infestation; (B) Middle infestation; (C) Flourishing of infestation; (D) Terminal of infestation.