The Sm core protein SmEb regulates salt stress responses through maintaining proper splicing of RCD1 pre-mRNA in Arabidopsis

Relevance and regulation of alternative splicing in plant secondary metabolism: current understanding and future directions

The secondary metabolism of plants is an essential life process enabling organisms to navigate various stages of plant development and cope with ever-changing environmental stresses. Secondary metabolites, abundantly found in nature, possess significant medicinal value. Among the regulatory mechanisms governing these metabolic processes, alternative splicing stands out as a widely observed post-transcriptional mechanism present in multicellular organisms. It facilitates the generation of multiple mRNA transcripts from a single gene by selecting different splicing sites. Selective splicing events in plants are widely induced by various signals, including external environmental stress and hormone signals. These events ultimately regulate the secondary metabolic processes and the accumulation of essential secondary metabolites in plants by influencing the synthesis of primary metabolites, hormone metabolism, biomass accumulation, and capillary density. Simultaneously, alternative splicing plays a crucial role in enhancing protein diversity and the abundance of the transcriptome. This paper provides a summary of the factors inducing alternative splicing events in plants and systematically describes the progress in regulating alternative splicing with respect to different secondary metabolites, including terpenoid, phenolic compounds, and nitrogen-containing compounds. Such elucidation offers critical foundational insights for understanding the role of alternative splicing in regulating plant metabolism and presents novel avenues and perspectives for bioengineering.

Alternative Splicing Plays a Crucial Role in the Salt Tolerance of Foxtail Millet

Foxtail millet is an important cereal crop that is relatively sensitive to salt stress, with its yield significantly affected by such stress. Alternative splicing (AS) widely affects plant growth, development, and adaptability to stressful environments. Through RNA-seq analysis of foxtail millet under different salt treatment periods, 2078 AS events were identified, and analyses were conducted on differential gene (DEG), differential alternative splicing gene (DASG), and overlapping gene. To investigate the regulatory mechanism of AS in response to salt stress in foxtail millet, the foxtail millet AS genes SiCYP19, with two AS variants (SiCYP19-a and SiCYP19-b), were identified and cloned. Yeast overexpression experiments indicated that SiCYP19 may be linked to the response to salt stress. Subsequently, we conducted overexpression experiments of both alternative splicing variants in foxtail millet roots to validate them experimentally. The results showed that, under salt stress, both SiCYP19-a and SiCYP19-b jointly regulated the salt tolerance of foxtail millet. Specifically, overexpression of SiCYP19-b significantly increased the proline content and reduced the accumulation of reactive oxygen species (ROS) in foxtail millet, compared to that in SiCYP19-a. This shows that SiCYP19-b plays an important role in increasing the content of proline and promoting the clearance of ROS, thus improving the salt tolerance of foxtail millet.

The first intron of EIJ1 confers a specific response to wounding and herbivore stresses

Plants are constantly exposed to different kinds of biotic stress, such as herbivore attack and wounding. To deal with these stresses, plants have evolved sophisticated defence mechanisms to protect themselves. Previously, we found that EIJ1 (EDS1-interacting J protein 1) plays a negative regulatory role in plant disease resistance in Arabidopsis thaliana. Follow-up studies revealed that EIJ1 specifically responds to wounding and herbivore stresses. The expression of EIJ1 was specifically induced by wounding or herbivore stress, as demonstrated by similar results in EIJ1 protein assay. Interestingly, GUS staining found that the promoter of EIJ1 is not involved in the induction of expression under wounding stress. Instead, we identified the first intron of EIJ1 as a key factor in response to wounding stress. Deleting the first intron of EIJ1 resulted in a loss of response to wounding stress in plants. Our results broaden the role of EIJ1 in plant resistance to biotic stress and provide new insights into plant responses to biotic stress.

RCD1 Promotes Salt Stress Tolerance in Arabidopsis by Repressing ANAC017 Activity

Plants have evolved diverse strategies to accommodate saline environments. More insights into the knowledge of salt stress regulatory pathways will benefit crop breeding. RADICAL-INDUCED CELL DEATH 1 (RCD1) was previously identified as an essential player in salt stress response. However, the underlying mechanism remains elusive. Here, we unraveled that Arabidopsis NAC domain-containing protein 17 (ANAC017) acts downstream of RCD1 in salt stress response, and its ER-to-nucleus transport is triggered by high salinity. Genetic and biochemical evidence showed that RCD1 interacts with transmembrane motif-truncated ANAC017 in the nucleus and represses its transcriptional activity. Transcriptome analysis revealed that genes associated with oxidation reduction process and response to salt stress are similarly dysregulated in loss-of-function rcd1 and gain-of-function anac017-2 mutants. In addition, we found that ANAC017 plays a negative role in salt stress response by impairing the superoxide dismutase (SOD) enzyme activity. Taken together, our study uncovered that RCD1 promotes salt stress response and maintains ROS homeostasis by inhibiting ANAC017 activity.