Periodic Reporting for period 1 - BACTEPEA (Unraveling the molecular dialogue in microbial-assisted plant growth in the presence of heavy metals)
Reporting period: 2020-05-01 to 2022-04-30
Deciphering the molecular interactions between plants and microorganisms under HM stress is necessary to provide new pathways for improved soil management. This project addresses a crucial objective in food security, i.e. the development of sustainable agricultural practices to control potentially adverse effects of HM exposure on plant health and growth.
Objectives of the project:
- To demonstrate the plant growth promotion capacity of the actinobacterial strain Micromonospora cremea CR30T on a highly valuable crop (Pisum sativum) in the presence and absence of HMs
- To identify genes implicated in P. sativum response to the presence of M. cremea CR30T
- To identify genes implicated in P. sativum response to HMs
- To identify genes implicated in P. sativum response to HMs in the presence of M. cremea CR30T
- To determine HM accumulation in P. sativum tissues in the presence and absence of M. cremea CR30T.
Greenhouse experiment: One of the major effects observed in HM-exposed P. sativum plants, even after a short period of exposure, was the reduction in the number of nodules developed at plant roots. Interestingly, this effect was reduced in CR30-inoculated plants. Pertaining to other growth parameters (number of leaves, chlorophyll intensity), no significant differences were detected between treatments. However, in HM-exposed plants, the presence of CR30 did result in an enhanced root and shoot development. The evolution of P. sativum plants was measured every week. At the end of the experiment, the observed differences between HM-treated plants and their respective controls were accentuated. Moreover, plant development was significantly influenced by the presence of CR30, which led to a considerable reduction of HM-induced adverse effects on plant growth.
HM concentrations in plant tissues: Heavy metal accumulation was detected in pea plants after ten days of irrigation with a solution containing several HMs. CR30-inoculated plants presented lower HM concentrations than non-inoculated plants, being this effect more pronounced in roots than in shoots. Accumulation values depended on the specific HM under analysis, with some of them being translocated to aerial plant parts while others were not. The analysis of shoot, root and nodule samples indicated that HM accumulation was dependent of the presence of CR30.
Transcriptomic analysis: In both the presence and absence of HMs, the transcriptomic profiles of CR30-inoculated plants showed an important number of differentially expressed genes (DEGs), with respect to non-inoculated control plants. Some of these DEGs are related to organelle organization and chromatin assembly. In addition, genes related to metabolic processes, including nitrogen metabolism, were identified. Other noteworthy genes that presented a differential expression had a gene ontology of response to stimuli, stress, defence, and binding. In CR30-inoculated HM-exposed plants, the number of DEGs compared to HM-exposed non-inoculated controls, was different, showing an increasing level of expression of the genes in the presence of CR30.
According to our transcriptomics results, several genes appear to be specifically expressed in the presence of CR30, being probably implicated in the root penetration process performed by this actinobacterial strain when inoculated to P. sativum plants. This finding will be the focus of future projects to better understand the different steps needed for CR30 colonization. This information could be of great interest to enhance plant colonization by other bacterial species. Finally, an important number of genes responded to HM exposure (including genes encoding HM transport and binding proteins), which will also be the focus of futures studies with potential interest for the field of metal phytoremediation.