ABSTRACT
Plant growth is severely harmed by cadmium (Cd) contamination, while the addition of zinc (Zn) can reduce the toxic effects of Cd. However, the interaction between Cd and Zn on the molecular mechanism and cell wall of Cosmosbipinnatus is unclear. In this study, a transcriptome was constructed using RNA-sequencing. In C. bipinnatus root transcriptome data, the expression of 996, 2765, and 3023 unigenes were significantly affected by Cd, Zn, and Cd + Zn treatments, respectively, indicating different expression patterns of some metal transporters among the Cd, Zn, and Cd + Zn treatments. With the addition of Zn, the damage to the cell wall was reduced, both the proportion and content of polysaccharides in the cell wall were changed, and Cd accumulation was decreased by 32.34%. In addition, we found that Cd and Zn mainly accumulated in pectins, the content of which increased by 30.79% and 61.4% compared to the CK treatment. Thus, Zn could alleviate the toxicity of Cd to C. bipinnatus. This study revealed the interaction between Cd and Zn at the physiological and molecular levels, broadening our understanding of the mechanisms of tolerance to Cd and Zn stress in cosmos.
ABSTRACT
Methyl jasmonate (MeJA), a crucial phytohormone, which plays an important role in resistance to Cadmium (Cd) stress. The cell wall (CW) of root system is the main location of Cd and plays a key role in resistance to Cd toxicity. However, the mechanism effect of MeJA on the CW composition and Cd accumulation remain unclear. In this study, the contribution of MeJA in regulating CW structure, pectin composition and Cd accumulation was investigated in Cosmos bipinnatus. Phenotypic results affirm MeJA's significant role in reducing Cd-induced toxicity in C. bipinnatus. Notably, MeJA exerts a dual impact, reducing Cd uptake in roots while increasing Cd accumulation in the CW, particularly bound to pectin. The molecular structure of pectin, mainly uronic acid (UA), correlates positively with Cd content, consistent in HC1 and cellulose, emphasizing UA as pivotal for Cd binding. Furthermore, MeJA modulates pectin methylesterase (PME) activity under Cd stress, influencing pectin's molecular structure and homogalacturonan (HG) content affecting Cd-binding capacity. Chelate-soluble pectin (CSP) within soluble pectins accumulates a substantial Cd proportion, with MeJA regulating both UA content and the minor component 3-deoxy-oct-2-ulosonic acid (Kdo) in CSP. The study delves into the intricate regulation of pectin monosaccharide composition under Cd stress, revealing insights into the CW's physical defense and Cd binding. In summary, this research provides novel insights into MeJA-specific mechanisms alleviating Cd toxicity in C. bipinnatus, shedding light on complex interactions between MeJA, and Cd accumulation in CW pectin polysaccharide.
