Periodic Reporting for period 4 - Sense2SurviveSalt (Surviving salinity: How do plants sense Na+?)
Période du rapport: 2022-07-01 au 2022-12-31
Globally, 6% of the arable land is affected by high salinity and the area of land affected by salinization is increasing by a rate of 3 hectares/min. Plant growth is highly responsive to increasing soil salinity (sodium chloride; NaCl) and results in severely hampered growth and crop yield. Enhanced salt tolerance in plants is therefore of key importance to ensure future food production to sustain the growing world population. Currently, several sodium-activated signalling cascades, such as the ‘Salt Overly Sensitive’ pathway, are described that prevent the toxic overaccumulation of sodium ions in plant cells. However, it is unknown how plants sense Na+ ions which lead to the activation of the signalling pathways, since there is no Na+ sensor described in plants. Identification of the sodium sensors in plants is fundamental to the understanding of plant sodium perception and tolerance. Additionally, this knowledge can be applied to commercially important plant species to improve salt tolerance in crops. The main aim of this project is to identify the Na+-sensing mechanism(s) in plants and explain how these result in the sodium specific responses observed in plants exposed to salinity stress.
Previously, a Genome-Wide Association Mapping Study (GWAS) identified several causal loci determining Na+-dependent root gravitropism. In-depth experiments using comprehensive microarray polymer profiling (CoMPP) analysis, confirmed that salt stress increases ExAD-dependent arabinosylation in Arabidopsis seedlings. exad mutants show increased root epidermal cell wall thickening mediating salt tolerance in plants. Using a newly developed timelapse setup spatio-temporal root growth dynamics could be quantified. New insights and results were published in a review paper (Zou, Zhang and Testerink, 2021, Plant, Cell and Environment doi: 10.1111/pce.14205) and a research paper (Zou et al., 2022, BioRxiv; in revision for publication https://www.biorxiv.org/content/10.1101/2022.06.22.497042v1 ).
In addition, the natural variation work was expanded by investigating detailed growth phases responses in a set of accessions, revealing a trade-off between maintenance of primary and lateral root development and growth when plants are exposed to salt. This work was published as Van Zelm et al., Plant, Cell and Environment, 2023 (doi: 10.1111/pce.14583). Moreover, by comparing with the halophyte species Schrenkiella parvula, we were able to identify this species as Na+-insensitive with respect to several root traits. This work was recently published as Li et al., New Phytologist 2023 (doi: 10.1111/nph.18873).
In addition, the natural variation work was expanded by investigating detailed growth phases responses in a set of accessions, revealing a trade-off between maintenance of primary and lateral root development and growth when plants are exposed to salt. This work was published as Van Zelm et al., Plant, Cell and Environment, 2023 (doi: 10.1111/pce.14583). Moreover, by comparing with the halophyte species Schrenkiella parvula, we were able to identify this species as Na+-insensitive with respect to several root traits. This work was recently published as Li et al., New Phytologist 2023 (doi: 10.1111/nph.18873).
We expanded our focus to the role of cell wall modifications in controlling salt stress responses. By using a set of different techniques, we detected changes at the cell wall structure level. Salt mostly affects the composition of the pectin moieties, determined by sodium dependent pectin methyl esterases (PMEs), likely altering cell wall mechanics and elasticity. Mutant lines involved in cell wall mechanics were ordered to further study the role of calcium signalling and cell wall mechanics during salt stress. We identified chemicals that alleviate most of salt-dependent stress responses, likely inhibiting PMEs, suggesting that salt activates PMEs induce certain salt stress phenotypes. Moreover, the salt-dependent cell wall changes are detected by known cell wall sensors which seem to be required for both early and late responses to salt. Using our timelapse setup, we monitored salt induced root growth responses in cell wall sensor mutants. This research has been recently published in Gigli-Bisceglia et al., 2022 (doi: 10.1242/dev.200363). Because recent observations highlighted that perception of biotic stress might allow plants to mount salt stress resilience pathways we wrote a review paper highlighting the possibility that salt sensing and pathogen perception mechanisms partially overlap (doi: 10.1016/j.pbi.2021.102120) . Our review figure was chosen as journal cover. To further characterize the salt sensitivity response, a second transcriptome analysis has been carried out including mutant lines with altered sodium sensitivity. These results have been published in the PhD thesis of Dr. Jasper Lamers (https://research.wur.nl/en/publications/this-is-the-way-how-plants-respond-to-salt ) and are currently being analysed in more depth to submit for publication to a peer-reviewed journal. We also published our view on root responses to water deficit and salinity in Testerink and Lamers, Nature 2022 (doi: 10.1038/d41586-022-04171-9).