Abstract
Abiotic stresses have a negative effect on crop production, affecting both vegetative and reproductive development. Ethylene plays a relevant role in plant response to environmental stresses, but the specific contribution of ethylene biosynthesis and signalling components in the salt stress response differs between Arabidopsis and rice, the two most studied model plants. In this paper, we study the effect of three gain-of-function mutations affecting the ethylene receptors CpETR1B, CpETR1A, and CpETR2B of Cucurbita pepo on salt stress response during germination, seedling establishment, and subsequent vegetative growth of plants. The mutations all reduced ethylene sensitivity, but enhanced salt tolerance, during both germination and vegetative growth, demonstrating that the three ethylene receptors play a positive role in salt tolerance. Under salt stress, etr1b, etr1a, and etr2b germinate earlier than WT, and the root and shoot growth rates of both seedlings and plants were less affected in mutant than in WT. The enhanced salt tolerance response of the etr2b plants was associated with a reduced accumulation of Na+ in shoots and leaves, as well as with a higher accumulation of compatible solutes, including proline and total carbohydrates, and antioxidant compounds, such as anthocyanin. Many membrane monovalent cation transporters, including Na+/H+ and K+/H+ exchangers (NHXs), K+ efflux antiporters (KEAs), high-affinity K+ transporters (HKTs), and K+ uptake transporters (KUPs) were also highly upregulated by salt in etr2b in comparison with WT. In aggregate, these data indicate that the enhanced salt tolerance of the mutant is led by the induction of genes that exclude Na+ in photosynthetic organs, while maintaining K+/Na+ homoeostasis and osmotic adjustment. If the salt response of etr mutants occurs via the ethylene signalling pathway, our data show that ethylene is a negative regulator of salt tolerance during germination and vegetative growth. Nevertheless, the higher upregulation of genes involved in Ca2+ signalling (CpCRCK2A and CpCRCK2B) and ABA biosynthesis (CpNCED3A and CpNCED3B) in etr2b leaves under salt stress likely indicates that the function of ethylene receptors in salt stress response in C. pepo can be mediated by Ca2+ and ABA signalling pathways.
Highlights
One of the great challenges facing agriculture today is the development of production systems that mitigate the deleterious effects of climate change, including drought and salinity[1]
In Arabidopsis and other plants, including maize and tomato, ethylene positively regulates salt stress tolerance[25,45,46,47], in other plant species, such as rice and tobacco, ethylene plays a negative role in salinity stress response[24,32]
We demonstrate that ethylene is involved in the salt stress response of C. pepo
Summary
One of the great challenges facing agriculture today is the development of production systems that mitigate the deleterious effects of climate change, including drought and salinity[1]. In arid and semi-arid areas, soil and water salinity constitute two of the most important abiotic. The primary effects of salinity are very similar to those caused by drought. A high concentration of salt in the soil reduces the plant’s ability to absorb water, known as the osmotic effect due to salinity. This leads to reduced absorption of essential elements, such as K+, Ca2+ and NO3−, and a toxic accumulation of Na+ and Cl− in aerial parts of the plant[3]. The accumulation of salt in leaf cells inhibits cell expansion and photosynthetic
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