The Roles of Calcineurin B-like Proteins in Plants under Salt Stress

Genome-wide identification of Rosa roxburghii CML family genes identifies an RrCML13-RrGGP2 interaction involved in calcium-mediated regulation of ascorbate biosynthesis

Calmodulin-like proteins (CMLs) are an essential family of calcium sensors involved in multiple Ca2+-mediated cellular processes in plants. Rosa roxburghii Tratt, known for the abundance of L-ascorbic acid (AsA) in its fruits, is widely distributed in calcium-rich soil of the karst region in southwestern China. The aim of this study was to identify key CMLs that respond to exogenous Ca2+ levels and regulate AsA biosynthesis in R. roxburghii. A genome-wide scan revealed the presence of 41 RrCML genes with 1-4 EF-hand motif (s) unevenly distributed across the 7 chromosomes of R. roxburghii. qRT-PCR analysis revealed that RrCML13, RrCML10, and RrCML36 responded significantly to exogenous Ca2+ treatment, and RrCML13 was positively correlated with GDP-L-galactose phosphorylase encoding gene (RrGGP2) expression and AsA content in the developing fruit. Overexpression of RrCML13 in fruits and roots significantly promoted the transcription of RrGGP2 and the accumulation of AsA, while virus-induced silencing of RrCML13 reduced the transcription of RrGGP2 and the content of AsA. Furthermore, Moreover, the yeast two-hybrid and bimolecular fluorescence complementation (BiFC) analysis confirmed the interaction between RrCML13 and RrGGP2 proteins, indicating that RrCML13 plays a regulatory role in calcium-mediated AsA biosynthesis. This study enhances our understanding of R. roxburghii CMLs and sheds light on the calcium-mediated regulation of AsA biosynthesis.

BnaPLDα1-BnaMPK6 Involved in NaCl-Mediated Overcoming of Self-Incompatibility in Brassica napus L

Self-incompatibility (SI) is an important genetic mechanism exploited by numerous angiosperm species to prevent inbreeding. This mechanism has been widely used in the breeding of SI trilinear hybrids of Brassica napus. The SI responses in these hybrids can be overcome by using a salt (NaCl) solution, which is used for seed propagation in SI lines. However, the mechanism underlying the NaCl-induced breakdown of the SI response in B. napus remains unclear. Here, we investigated the role of two key proteins, BnaPLDα1 and BnaMPK6, in the breakdown of SI induced by NaCl. Pollen grain germination and seed set were reduced in BnaPLDα1 triple mutants following incompatible pollination with NaCl treatment. Conversely, SI responses were partially abolished by overexpression of BnaC05.PLDα1 without salt treatment. Furthermore, we observed that phosphatidic acid (PA) produced by BnaPLDα1 bound to B. napus BnaMPK6. The suppression and enhancement of the NaCl-induced breakdown of the SI response in B. napus were observed in BnaMPK6 quadruple mutants and BnaA05.MPK6 overexpression lines, respectively. Moreover, salt-induced stigmatic reactive oxygen species (ROS) accumulation had a minimal effect on the NaCl-induced breakdown of the SI response. In conclusion, our results demonstrate the essential role of the BnaPLDα1-PA-BnaMPK6 pathway in overcoming the SI response to salt treatment in SI B. napus. Additionally, our study provides new insights into the relationship between SI signaling and salt stress response. SIGNIFICANCE STATEMENT: A new molecular mechanism underlying the breakdown of the NaCl-induced self-incompatibility (SI) response in B. napus has been discovered. It involves the induction of BnaPLDα1 expression by NaCl, followed by the activation of BnaMPK6 through the production of phosphatidic acid (PA) by BnaPLDα1. Ultimately, this pathway leads to the breakdown of SI. The involvement of the BnaPLDα1-PA-BnaMPK6 pathway in overcoming the SI response following NaCl treatment provides new insights into the relationship between SI signalling and the response to salt stress.

The Role of PGPB-Microalgae interaction in Alleviating Salt Stress in Plants

Plant development and yield are severely hampered by climate change. Plants are very prone to a variety of abiotic stressors during growth, making them susceptible to destruction which can reduce the productivity by 20-60%. These stresses generate reactive oxygen species (ROS), which damage lipids, proteins, and nucleic acids. Microalgae and plant growth-promoting bacteria (PGPB) are remarkably effective at reducing the effects of salt stress and promoting plant growth, thereby increasing agricultural yield, and helping ensure global food security. Through a variety of mechanisms, including the production of phytohormones, 1-aminocyclopropane-1-carboxylic acid deaminase, exopolysaccharide, siderophores, hydrogen cyanide, extracellular polymeric substances, volatile organic compounds, and modulation of antioxidants defense machinery under abiotic stresses promote plant growth after inoculation of PGPB and microalgae. These microorganisms also maintain ion homeostasis, offer osmotic balance, stimulate genes that respond to salt and drought, rewire the metabolism, modify the transcription of ion transporter genes, and more. To counteract the negative consequences of salinity stress, this study summarizes the effects of PGPB- microalgae along with a tentative protective mechanism during salinity stress for sustainable agriculture.

Effects of Exogenous Isosteviol on the Physiological Characteristics of Brassica napus Seedlings under Salt Stress

In this paper, the effect of isosteviol on the physiological metabolism of Brassica napus seedlings under salt stress is explored. Brassica napus seeds (Qinyou 2) were used as materials, and the seeds were soaked in different concentrations of isosteviol under salt stress. The fresh weight, dry weight, osmotic substance, absorption and distribution of Na+, K+, Cl-, and the content of reactive oxygen species (ROS) were measured, and these results were combined with the changes shown by Fourier transform infrared spectroscopy (FTIR). The results showed that isosteviol at an appropriate concentration could effectively increase the biomass and soluble protein content of Brassica napus seedlings and reduce the contents of proline, glycine betaine, and ROS in the seedlings. Isosteviol reduces the oxidative damage to Brassica napus seedlings caused by salt stress by regulating the production of osmotic substances and ROS. In addition, after seed soaking in isosteviol, the Na+ content in the shoots of the Brassica napus seedlings was always lower than that in the roots, while the opposite was true for the K+ content. This indicated that under salt stress the Na+ absorbed by the Brassica napus seedlings was mainly accumulated in the roots and that less Na+ was transported to the shoots, while more of the K+ absorbed by the Brassica napus seedlings was retained in the leaves. It is speculated that this may be an important mechanism for Brassica napus seedlings to relieve Na+ toxicity. The spectroscopy analysis showed that, compared with the control group (T1), salt stress increased the absorbance values of carbohydrates, proteins, lipids, nucleic acids, etc., indicating structural damage to the plasma membrane and cell wall. The spectra of the isosteviol seed soaking treatment group were nearly the same as those of the control group (T1). The correlation analysis shows that under salt stress the Brassica napus seedling tissues could absorb large amounts of Na+ and Cl- to induce oxidative stress and inhibit the growth of the plants. After the seed soaking treatment, isosteviol could significantly reduce the absorption of Na+ by the seedling tissues, increase the K+ content, and reduce the salt stress damage to the plant seedlings. Therefore, under salt stress, seed soaking with isosteviol at an appropriate concentration (10-9~10-8 M) can increase the salt resistance of Brassica napus seedlings by regulating their physiological and metabolic functions.