Genome-wide identification of Shaker K+ channel family in Nicotiana tabacum and functional analysis of NtSKOR1B in response to salt stress

Rhizosphere microorganisms mediate ion homeostasis in cucumber seedlings: a new strategy to improve plant salt tolerance

BACKGROUND

Soil salinization is a formidable challenge for vegetable production, primarily because of the detrimental effects of ion toxicity. Rhizosphere microorganisms promote plant growth and bolster salt tolerance, but the extent to which microbial communities can increase plant resilience by regulating ion homeostasis under salt stress remains underexplored. The goal of this study was to enrich microbial communities from the rhizosphere of salt-stressed cucumber seedlings and identify their impact on ion balance and plant growth under saline conditions.

RESULTS

Salt stress induced significant alterations in the composition, structure, and function of the root-associated microbial community. Compared with a 75 mM NaCl treatment alone, inoculation with salt-induced rhizosphere microorganisms (SiRMs) under the same conditions significantly increased the growth of cucumber seedlings; plant height increased by 61.3%, and the fresh weights of the shoots and roots increased by 45.3% and 38.9%, respectively. Moreover, superoxide dismutase (SOD) activity increased by 4.1%, and peroxidase (POD) activity and superoxide anion (O2·-) content decreased by 10.5% and 3.7%, respectively. In the roots, stems, and leaves of cucumber seedlings treated with SiRMs and 75 mM NaCl, the Na+ content was significantly reduced by 15.8%, 18.9%, and 9.7%, respectively. Conversely, the K+ content significantly increased by 32.7%, 16.9%, and 28.8%, respectively. Under salt stress conditions, inoculation with SiRMs significantly increased the rate of Na+ expulsion in the roots of cucumber seedlings by 18.3%, but the K+ expulsion rate decreased by 76.7%. These dynamic changes are attributed to the upregulation of genes such as CsHKT1, CsHAK5, and CsCHX18;4.

CONCLUSIONS

Enrichment with SiRMs played a pivotal role in maintaining ion homeostasis and significantly enhanced the salt tolerance of cucumber seedlings. These findings highlight the potential for microbial-assisted strategies to mitigate the adverse effects of soil salinity and provide valuable insights into the complex interplay between the microbial community and plant resilience from the perspective of ion balance.

A P450 superfamily member NtCYP82C4 promotes nicotine biosynthesis in Nicotiana tabacum

In plants, cytochrome P450s are monooxygenase that play key roles in the synthesis and degradation of intracellular substances. In tobacco, the majority of studies examining the P450 superfamily have concentrated on the CYP82E subfamily, where multiple family members function as demethylases, facilitating the synthesis of nornicotine. In this study, NtCYP82C4, a tobacco P450 superfamily member, was identified from a gene-edited tobacco mutant that nicotine biosynthesis in tobacco leaves is evidently reduced. Compared to the wild-type plants, the knockout of NtCYP82C4 resulted in a significantly lower nicotine content and biomass in tobacco leaves. Transcriptome and metabolome analyses indicated that the knockout of NtCYP82C4 inhibites secondary metabolic processes in tobacco plants, leading to the accumulation of some important precursors in the nicotine synthesis process, including aspartic acid and nicotinic acid, and increases nitrogen partitioning associated with those processes such as amino acid synthesis and utilization. It is speculated that NtCYP82C4 may function as an important catalase downstream of the nicotine synthesis. Currently, most of the steps and enzymes involved in the nicotine biosynthesis process in tobacco have been elucidated. Here, our study deepens the current understanding of nicotine biosynthesis process and provides new enzyme targets for nicotine synthesis in tobacco plants.