The Molecular Mechanism and Effects of Root Pruning Treatment on Blueberry Tree Growth

Abstract

Root pruning can promote the transplanting of young green plants, but the overall impact of pruning on root growth, morphology, and physiological functions remains unclear. This study integrated transcriptomics and physiological analyses to elucidate the effects of root pruning on blueberry growth. Appropriate pruning (CT4) significantly promoted plant growth, with above-ground biomass and leaf biomass significantly increasing compared to the control group within 42 days. Photosynthesis temporarily decreased at 7 days but recovered at 21 and 42 days. Transcriptomics analysis showed that the cellulose metabolism pathway was rapidly activated and influenced multiple key genes in the starch metabolism pathway. Importantly, transcription factors associated with vascular development were also significantly increased at 7, 21, and 42 days after root pruning, indicating their role in regulating vascular differentiation. Enhanced aboveground growth was positively correlated with the expression of photosynthesis-related genes, and the transport of photosynthetic products via vascular tissues provided a carbon source for root development. Thus, root development is closely related to leaf photosynthesis, and changes in gene expression associated with vascular tissue development directly influence root development, ultimately ensuring coordinated growth between aboveground and belowground parts. These findings provide a theoretical basis for optimizing root pruning strategies to enhance blueberry growth and yield.

Keywords: root growth; root pruning; transcriptome; vascular tissue development.

Figure 1

Effects of root pruning on plant physiology in blueberry plants. Plant height (A), leaf area (B), stem basal diameter (C), leaf dry weight (D), stem dry weight (E), and root dry weight (F) 56 days after root pruning. Data are presented as the mean ± standard error (each group includes three biologically independent plants). Different lowercase letters indicate significant differences between groups (one-way ANOVA, p < 0.05). CK, control group (no root pruning); CT2, 20% root pruning; CT4, 40% root pruning; CT5, 50% root pruning; CT6, 60% root pruning; CT8, 80% root pruning.

Figure 2

Morphological and biomass changes in the root systems of blueberry plants after root pruning. Phenotypic changes related to the growth and development of CT4 blueberry plants on days 7, 21, and 42 after root pruning (A). (CK) were the control, CT4 was 40% root pruning. Seeding height (B), stem basal diameter (C), and leaf area (D) of blueberry plants 7, 21, and 42 days after root pruning. Dry weight (E) and water content (F) of roots, stems, and leaves, respectively, on day 42 of root pruning. Data are presented as the mean ± standard error (each group contains three biologically independent plants). Different capital letters in the figure indicate significant differences between the same treatment at different time points (one-way analysis of variance, p < 0.05). Different lowercase letters indicate significant differences between different treatments at the same time point (p < 0.05). Vertical bars indicate standard error.

Figure 3

Photosynthetic function of blueberry plants after root pruning. Photosynthetic rate (A), stomatal conductance (B), intercellular CO₂ (C), transpiration rate (D), F_v/F_m (E), ΦPSII (F), and NPQ (G) on days 7, 21, and 42 after root pruning. Data are presented as the mean ± standard error (each group contains three biologically independent plants). Different capital letters in the figure indicate significant differences between the same treatment at different time points (one-way analysis of variance, p < 0.05). At each time point, between-group differences were analyzed using unpaired Student’s t-tests and corrected using Bonferroni correction. Different lowercase letters indicate significant differences between different treatments at the same time point (p < 0.05). Vertical bars indicate the standard error.

Figure 4

Enrichment of DEGs in KEGG pathways in blueberry leaves and roots during T1, T2, and T3. KEGG enrichment analysis of DEGs in blueberry leaves: CK-T1 vs. CT-T1 (A), CK-T2 vs. CT-T2 (B), and CK-T3 vs. CT-T3 (C). KEGG enrichment analysis of DEGs in blueberry roots: CK-T1 vs. CT-T1 (D), CK-T2 vs. CT-T2 (E), and CK-T3 vs. CT-T3 (F).

Figure 5

Analysis of metabolic pathways associated with vascular tissue development. Analysis of DEGs related to starch and sucrose metabolic pathways (A). Analysis of DEGs associated with carbon metabolic pathways (B). Used to synthesize UDP-glucose, a substrate for cellulose synthesis. The three stages of root development after blueberry root pruning are presented in the heatmap, from left to right, CK-T1 (CK-7d), CK-T2 (CK-21d), CK-T3 (CK-42d), CT-T1 (CT4-7d), CT-T2 (CT4-21d), and CT-T3 (CT4-42d). The data presented in the heatmap is the average of three biological replicates. Enzyme reactions associated with gene expression involving each step are presented on the corresponding arrows, containing glucoside hydrolase (BGLU), sucrose invertase (INV), and granule-bound starch synthase (WAXY). The gene expressions involved were BGLU (Vadar_g18328, Vadar_g18327, Vadar_g39897, Vadar_g39093, Vadar_g228 and Vadar_g25404), INV (Vadar_g16537), and WAXY (Vadar_g15976). (B) Analysis of DEGs related to carbon metabolic pathways. The data presented in the heatmap are the average of three biological replicates. Enzyme reactions associated with gene expression involving each step are presented on the corresponding arrows, containing (Diphosphate-dependent phosphofructokinase, PFP), (Glyceraldehyde-3-phosphate dehydrogenase, GAPN), (Glyceraldehyde 3-phosphate dehydrogenase, GAPA), (Dihydrolipoyl dehydrogenase, DLD), and (Malate dehydrogenase, MDH2). The gene expressions involved were PFP (Vadar_g33626), GAPN (Vadar_g28061), GAPA (Vadar_g39062), DLD (Vadar_g11578), and MDH2 (Vadar_g46714). CK, non-root pruning; CT, root pruning.

Figure 6

Heat map of transcription factors associated with root vascular tissue development after root pruning. The color scale bar in the top-right corner represents an increase (red), a decrease (blue), and no change (yellow) in gene expression. Sampling was performed 7 days (T1), 21 days (T2), and 42 days (T3) after root pruning, as indicated by the English subscripts in the figure. The gene expressions involved were VcVND6 (Vadar_g5252), VcVND6 (Vadar_g16528), VcVND7 (Vadar_g26196), VcE2Fc (Vadar_g23325), VcHB15 (Vadar_g37392), VcPHB (Vadar_g6161), VcMYB46 (Vadar_g39307), VcMYB46 (Vadar_g22345), VcKNAT7 (Vadar_g5151), VcVNI2 (Vadar_g45099), VcXND1 (Vadar_g1180), VcNST1 (Vadar_g9575), VcSND1 (Vadar_g38770), VcPHV (Vadar_g3231), and VcPHV (Vadar_g41490). CK, non-root pruning; CT, root pruning.

Figure 7

Analysis of metabolic pathways associated with root pruning and photosynthesis. (A) Analysis of DEGs associated with the photosynthetic pathway. The data presented in the heatmap is the average of three biological replicates. Enzyme reactions associated with gene expression involving each step are presented on the corresponding arrows containing cytochrome c6 and Pet J. The gene expression involved in this process was Pet J (Vadar_g7406). (B) Analysis of DEGs associated with carbon metabolism and tricarboxylic acid cycle pathways. The data presented in the heatmap are the average of three biological replicates. Enzyme reactions associated with gene expression involving each step are presented on the corresponding arrows, containing aldose 1-epimerase (GALM), dihydrolipoyl dehydrogenase (DLD), and malate dehydrogenase (MDH2). The genes involved were GALM (Vadar_g20155 and Vadar_g20154), DLD (Vadar_g11578), and MDH2 (Vadar_g46714). CK, non-root pruning; CT, root pruning.

Figure 8

Validation of key genes related to vascular tissue development and photosynthesis in the roots and leaves of control and CT4 groups by qRT-PCR using actin as the reference gene. The column represents the results of qRT-PCR, with the coordinate axis on the left. The line represents the results of the transcriptome, with the coordinate axis on the right.

Figure 9

Schematic illustration of the coordinated development of the aboveground and underground parts of blueberry after root pruning.