The impact of salt stress on the physiology and the transcriptome of the model streptophyte green alga Chara braunii

Abstract

Chara braunii is a model for early land plant evolution and terrestrialization. Salt stress has a profound effect on water and ion transport activities, thereby interacting with many other processes, including inorganic carbon acquisition for photosynthesis. In this study, we analyzed the impact of salt stress (5 practical salt units, PSU) on the physiology and gene expression in C. braunii. Photosynthesis was only slightly affected 6 h after salt addition and returned to control levels after 48 h. Several organic compounds such as proline, glutamate, sucrose, and 2‐aminobutyrate accumulated in salt‐treated thalli and might contribute to osmotic potential acclimation, whereas the amount of K+ decreased. We quantified transcript levels for 17,387 genes, of which 95 were up‐regulated and 44 down‐regulated after salt addition. Genes encoding proteins of the functional groups ion/solute transport and cell wall synthesis/modulation were enriched among the up‐regulated genes 24–48 h after salt stress, indicating their role in osmotic acclimation. However, a homolog to land plant ERD4 osmosensors was transiently upregulated after 6 h, and phylogenetic analyses suggested that these sensors evolved in Charophyceae. Down‐regulated genes were mainly related to photosynthesis and carbon metabolism/fixation, consistent with the observed lowered growth after extended cultivation. The changed expression of genes encoding proteins for inorganic carbon acquisition might be related to the impact of salt on ionic relations and inorganic carbon uptake. The results indicate that C. braunii can tolerate enhanced salt concentrations in a defined acclimation process, including distinct gene expression changes to achieve new metabolic homeostasis.

OsMGD1-Mediated Membrane Lipid Remodeling Improves Salt Tolerance in Rice

“…Salt stress commonly causes reduced water uptake in leaves, which limits stomatal opening and blocks electron transfer; together, these effects reduce photosynthetic efficiency and can even lead to plant death [ 4 , 6 ]. Despite some salt-tolerant plants reducing transpiration through lower stomatal conductance to conserve water, this usually impairs photosynthetic CO 2 assimilation [ 41 ].…”

“…It is estimated that approximately 20% of the cultivated land and 50% of the irrigated farmland worldwide will be affected by salt stress by the middle of this century [ 3 ]. In salt-affected farmland, crops take up excess Na + and Cl − ions, causing ion toxicity, osmotic stress, oxidative stress, and severe impairment of photosynthetic capacity, which ultimately lead to a reduction in yield [ 4 , 5 , 6 ]. However, with the world population projected to reach 9.6 billion by 2050, the challenge of avoiding food shortages requires at least a 70% increase in food production from current levels [ 7 ].…”