Effects of α-Naphthylacetic Acid on Cadmium Stress and Related Factors of Tomato by Regulation of Gene Expression

Abstract

Cadmium (Cd) is absorbed and accumulated by crops, and it adversely affects plant growth and development. To explore the effect of exogenous auxin on Cd stress, we applied different concentrations of α-naphthaleneacetic acid (NAA) and the auxin transport inhibitor 2,3,5-triiodobenzoic acid (TIBA) to tomato plants exposed to Cd stress in a hydroponic system. NAA and TIBA at different concentrations were used under Cd stress. Plant growth, root morphology, and auxin distribution were observed. Lipid peroxidation and antioxidant enzyme activities in leaves, cadmiumcontent, and migration coefficient of plants were determined. Transcriptome sequencing and qRT-PCR were used to analyze the differentially expressed genes. Results showed that auxin was concentrated in the leaf veins, stem base, and roots in P5::GUS “Chico III” transgenic tomato, indicating NAA polar transport to the roots and promotion of root growth under Cd stress. Cd was absorbed by the roots and transported to the shoots. It then inhibited plant growth and promoted antioxidant enzyme activities, O2− production, H2O2 accumulation, and membrane lipid peroxidation. Treatment with 0.5 μM NAA improved antioxidant enzyme activities, reduced reactive oxygen, maintained membrane permeability, and decreased malondialdehyde and proline contents. Transcriptome analysis revealed that NAA activated a large number of genes in the roots: 1998 genes were differentially expressed in response to Cd or NAA treatment, and 1736 genes were specifically expressed in response to NAA treatment under Cd stress. Among the differentially expressed genes, tomato metallocarboxypeptidase inhibitor TCMP-2 (2A11) and Solanum lycopersicum heavy metal-associated isoprenylated plant protein (HIPP) 7-like (LOC101264884), which are closely related to plant response to heavy metal stress, may be the key sites of NAA. In conclusion, the NAA-mediated response to Cd stress was closely associated with “defense response” genes in shoots and “oxidoreductase activity, oxidizing metal ions” and “response to auxin” genes in roots.

Comprehensive Analysis of BrHMPs Reveals Potential Roles in Abiotic Stress Tolerance and Pollen–Stigma Interaction in Brassica rapa

“…It is composed of ~30 amino acid residues and contains two cysteine residues that bind and transfer heavy metal ions such as cadmium, zinc, cobalt and copper [ 28 ]. Genes containing the HMA structural domain may function in abiotic stresses, plant development, and immunity [ 17 , 29 , 30 ]. Motif 8 and motif 10 were identified as HAD (haloacid dehalogenase) structural domains (accession: cl21460).…”

“…AtHIPP3 regulates the salicylic acid-dependent pathogen response pathway through its bound zinc and is also implicated in seed and flower development, with particular attention to the fact that the overexpression of HIPP3 delays flowering [ 16 ]. In Solanum lycopersicum , HIPP7, a possible key site for 1-naphthaleneacetic acid (NAA), co-regulates heavy metal stress [ 17 ]. These studies suggest that HMPs participate in heavy metal transport, detoxification, and response to abiotic stresses, with the potential for functions in sexual reproduction.…”

Carboxypeptidase inhibitors from Solanaceae as a new subclass of pathogenesis related peptide aiming biotechnological targets for plant defense

“…These characteristics indicate their potential role in plant defense mechanisms. Interestingly, the tomato CPI has already been implicated in responding to abiotic stress and shows increased expression levels after pathogen infection, suggesting its role as defense agent ( Slezina et al, 2021 ; Guan et al, 2022 ). It is worth noting that these features are similar to antimicrobial peptides and plant pathogenesis related proteins, which are known to be involved in plant defense.…”