Alterations in the root phenylpropanoid pathway and root-shoot vessel system as main determinants of the drought tolerance of a soybean genotype

Abstract

Climate change increases precipitation variability, particularly in savanna environments. We have used integrative strategies to understand the molecular mechanisms of drought tolerance, which will be crucial for developing improved genotypes. The current study compares the molecular and physiological parameters between the drought-tolerant Embrapa 48 and the sensitive BR16 genotypes. We integrated the root-shoot system's transcriptome, proteome, and metabolome to understand drought tolerance. The results indicated that Embrapa 48 had a greater capacity for water absorption due to alterations in length and volume. Drought tolerance appears to be ABA-independent, and IAA levels in the leaves partially explain the higher root growth. Proteomic profiles revealed up-regulated proteins involved in glutamine biosynthesis and proteolysis, suggesting osmoprotection and explaining the larger root volume. Dysregulated proteins in the roots belong to the phenylpropanoid pathways. Additionally, PR-like proteins involved in the biosynthesis of phenolics may act to prevent oxidative stress and as a substrate for modifying cell walls. Thus, we concluded that alterations in the root-shoot conductive vessel system are critical in promoting drought tolerance. Moreover, photosynthetic parameters from reciprocal grafting experiments indicated that the root system is more essential than the shoots in the drought tolerance mechanism. Finally, we provided a comprehensive overview of the genetic, molecular, and physiological traits involved in drought tolerance mechanisms.

Supplementary information: The online version contains supplementary material available at 10.1007/s12298-023-01307-7.

Keywords: Grafting assays; Phosphoproteome; Phytohormones; Proteome; Water use efficiency; Xylem caliber.

Fig. 1

Relative water content (RWC) of soybean plants under regular irrigation and drought stress. (A) An overview of the plants fourteen days after the reduction in the water supply of Embrapa 48 and BR16 genotypes under irrigated (I) and non-irrigated (NI) conditions. Relative water content RWC (%) of the leaves in (B) and in (C) of the roots. Bars represent the mean ± standard error (n = 5, where n represents the number of plants). Different capital letters indicate significant differences between means of the same treatment in different genotypes. Lowercase letters show significant differences between means within the same genotype under different treatments (t-test, p < 0.05)

Fig. 2

Morphological alterations in soybean roots under regular irrigation and drought conditions. In (A) soil moisture contents [h(%)] for the BR16 and Embrapa 48 genotypes. In (B), variations in the water volumes (V) added to pots and in the weight of the pots (ΔP) during the drought experiment. Variations in the root lengths (%) in (C) and the root volumes in (D). In (E) an overview at the end of the experiment of the roots from the Embrapa 48 and BR16 genotypes under irrigated I and non-irrigated conditions (NI, − 1.0 MPa). Bars represent the mean ± standard error (n = 5, where n represents the number of plants). Different capital letters indicate significant differences between means of the same treatment in different genotypes. Lowercase letters show significant differences between means within the same genotype under different treatments (t-test, p < 0.05)

Fig. 3

Absolute abundances of phytohormones and proline from soybean leaves and roots of the Embrapa 48 and BR16 genotypes under irrigation and drought (− 1.0 MPa) conditions. Bars represent the mean ± standard error (n = 5, where n represents the number of plants). Different capital letters indicate significant differences between means of the same treatment in different genotypes. Lowercase letters show significant differences between means within the same genotype under different treatments (t-test, p < 0.05)

Fig. 4

Effect of the drought stress on the net photosynthetic rate A in (A), stomatal conductance gs in (B), ratio Ci /Ca in (C), transpiratory rate E in (D) of the grafted plants. Legends represent: Plants with the root system from non-grafted Embrapa 48 plants (Emb48); with the root system from Embrapa 48 and shoot from BR 16 (Emb48_BR16); with the root system from non-grafted BR16 (BR16); with the root system from BR16 and shoot from Embrapa 48 (BR16_Embr48). Bars represent the mean ± standard error (n = 5, where n represents the number of plants). Different capital letters indicate significant differences between means of the same treatment in different genotypes. Lowercase letters show significant differences between means within the same genotype under different treatments (Tukey, p < 0.05)

Fig. 5

Effect of water deficit on the rate of electron transport (ETR) in the grafted soybean genotypes. Plants with root system from non-grafted Embrapa 48 plants (Emb48); with root system from Embrapa 48 and shoot from BR16 (Emb48_BR16); with the root system from non-grafted BR16 (BR16); with the root system from BR16 and shoot from Embrapa 48 (BR16_Embr48). Bars represent the mean ± standard error (n = 5, where n represents the number of plants). Different capital letters indicate significant differences between means of the same treatment in different genotypes. Lowercase letters show significant differences between means within the same genotype under different treatments (Tukey, p < 0.05)

Fig. 6

Effect of water deficit on the potential quantum efficiency of photosystem II Fv/Fm in (A), effective quantum yield of FSII ΦPSII in (B), non-photochemical extinction coefficient NPQ in (C), the fraction of absorbed light that is not thermally dissipated or used in the photochemical phase of FSII PE in (D), absorbed light fraction that is thermally dissipated D in (E) and absorbed light fraction that is used in the photochemical phase of FSII P in (F) grafted soybean plants. Plants with root system from non-grafted Embrapa 48 plants (Emb48); with root system from Embrapa 48 and shoot from BR16 (Emb48_BR16); with system root non-grafted BR16 (BR16); with root system from BR16 and shoot from Embrapa 48 (BR16_Embr48). Bars represent the mean ± standard error (n = 5, where n represents the number of plants). Different capital letters indicate significant differences between means of the same treatment in different genotypes. Lowercase letters show significant differences between means within the same genotype under different treatments (Tukey, p < 0.05)

Fig. 7

Analysis of the metabolite profiles from soybean roots by LC/MS. All runs were aligned using XCMS algorithm in (C) and the intensities of the ions were compared in (A) and the metabolic pathway analysis was performed using MetaboAnalyst platform in (B). Colored boxes by green, yellow and red in (A) correspond to the ions belongings to the pathways assigned in the (B). The m/z of the ions showed in (A) are the average values of 4 replicates

Fig. 8

Normalized relative abundances of some ions showing alterations in the tolerant genotype Embrapa 48 under normal irrigation (I) and drought (NI). Putative identifications (Supplementary material) were obtained for: M281T51—4,7-Dimethyl-3-(4-methoxyphenyl)coumarin; M353T55—4,7-Dimethyl-3-(4-methoxyphenyl)coumarin derivative; M353T49—3′,4′-Dimethoxy-7-hydroxyisoflavone derivative; M337T49—2-Hydroxy-2′,4′,6′-trimethoxychalcone derivative; M281T61—6-Ethoxy-4-methyl-3-phenylcoumarin; M281T51—6-Ethoxy-4-methyl-3-phenylcoumarin; M271T29- 3,6,4′-Trihydroxyflavone; M519T29—6″-O-Malonylgenistin; M503T23—6″-O-Malonyldaidzin; M255T59—Dadzein; M417T19—4′,7-hydroxyisoflavone-7-glucoside; M269T39—Genistein

Fig. 9

Light microscopy of the xylem vessels from the root system of the drought-tolerant Embrapa 48 and drought-sensitive BR16 under regular irrigation and drought conditions (− 1.0 MPa). The transversal sections show the xylem lumens in (A–D). Quantifications of the vessel number in (E), of the diameter of the vessel lumen in (F) and the vessel lumen total area in (G) from the root xylem

Fig. 10

Comprehensive overview of the genetic, molecular, and physiological responses of the drought-sensitive soybean genotype Embrapa 48 related to the parental drought-sensitive BR16 under drought stress conditions. Arrows inside the boxes indicate increases or decreases in experimentally evaluated parameters in the genotype Embrapa 48 compared to BR16. The number between parenthesis corresponds to the bibliographic references for each experimental result indicated in the boxes. (1) Oya et al. and Carvalho et al. ; (2) Mesquita et al. ; (3) Lima et al. ; (4) Coutinho et al. ; (5) this work