SlBIR3 Negatively Regulates PAMP Responses and Cell Death in Tomato

Identification and characterization of the plasma membrane H+-ATPase genes in Brassica napus and functional analysis of BnHA9 in salt tolerance

As a primary proton pump, plasma membrane (PM) H+-ATPase plays critical roles in regulating plant growth, development, and stress responses. PM H+-ATPases have been well characterized in many plant species. However, no comprehensive study of PM H+-ATPase genes has been performed in Brassica napus (rapeseed). In this study, we identified 32 PM H+-ATPase genes (BnHAs) in the rapeseed genome, and they were distributed on 16 chromosomes. Phylogenetical and gene duplication analyses showed that the BnHA genes were classified into five subfamilies, and the segmental duplication mainly contributed to the expansion of the rapeseed PM H+-ATPase gene family. The conserved domain and subcellular analyses indicated that BnHAs encoded canonical PM H+-ATPase proteins with 14 highly conserved domains and localized on PM. Cis-acting regulatory element and expression pattern analyses indicated that the expression of BnHAs possessed tissue developmental stage specificity. The 25 upstream open reading frames with the canonical initiation codon ATG were predicted in the 5' untranslated regions of 11 BnHA genes and could be used as potential target sites for improving rapeseed traits. Protein interaction analysis showed that BnBRI1.c associated with BnHA2 and BnHA17, indicating that the conserved activity regulation mechanism of BnHAs may be present in rapeseed. BnHA9 overexpression in Arabidopsis enhanced the salt tolerance of the transgenic plants. Thus, our results lay a foundation for further research exploring the biological functions of PM H+-ATPases in rapeseed.

PHB3 interacts with BRI1 and BAK1 to mediate brassinosteroid signal transduction in Arabidopsis and tomato

Brassinosteroids (BRs) are plant hormones that are essential in plant growth and development. BRASSINOSTEROID-INSENSITIVE 1 (BRI1) and BRI1 ASSOCIATED RECEPTOR KINASE 1 (BAK1), which are located on the plasma membrane, function as co-receptors that accept and transmit BR signals. PROHIBITIN 3 (PHB3) was identified in both BRI1 and BAK1 complexes by affinity purification and LC-MS/MS analysis. Biochemical data showed that BRI1/BAK1 interacted with PHB3 in vitro and in vivo. BRI1/BAK1 phosphorylated PHB3 in vitro. When the Thr-80 amino acid in PHB3 was mutated to Ala, the mutant protein was not phosphorylated by BRI1 and the mutant protein interaction with BRI1 was abolished in the yeast two-hybrid assay. BAK1 did not phosphorylate the mutant protein PHB3T54A . The loss-of-function phb3 mutant showed a weaker BR signal than the wild-type. Genetic analyses revealed that PHB3 is a BRI1/BAK1 downstream substrate that participates in BR signalling. PHB3 has five homozygous in tomato, and we named the closest to AtPHB3 as SlPHB3.1. Biochemical data showed that SlBRI1/SlSERK3A/SlSERK3B interacted with SlPHB3.1 and SlPHB3.3. The CRISPR-Cas9 method generated slphb3.1 mutant led to a BR signal stunted relatively in tomatoes. PHB3 is a new component of the BR signal pathway in both Arabidopsis and tomato.

Brassinosteroid Signaling Downstream Suppressor BIN2 Interacts with SLFRIGIDA-LIKE to Induce Early Flowering in Tomato

Brassinosteroid (BR) signaling is very important in plant developmental processes. Its various components interact to form a signaling cascade. These components are widely studied in Arabidopsis; however, very little information is available on tomatoes. Brassinosteroid Insensitive 2 (BIN2), the downstream suppressor of BR signaling, plays a critical role in BR signal pathway, while FRIGIDA as a key suppressor of Flowering Locus C with overexpression could cause early flowering; however, how the BR signaling regulates FRIGIDA homologous protein to adjust flowering time is still unknown. This study identified 12 FRIGIDA-LIKE proteins with a conserved FRIGIDA domain in tomatoes. Yeast two-hybrid and BiFC confirmed that SlBIN2 interacts with 4 SlFRLs, which are sub-cellularly localized in the nucleus. Tissue-specific expression of SlFRLs was observed highly in young roots and flowers. Biological results revealed that SlFRLs interact with SlBIN2 to regulate early flowering. Further, the mRNA level of SlBIN2 also increased in SlFRL-overexpressed lines. The relative expression of SlCPD increased upon SlFRL silencing, while SlDWF and SlBIN2 were decreased, both of which are important for BR signaling. Our research firstly provides molecular evidence that BRs regulate tomato flowering through the interaction between SlFRLs and SlBIN2. This study will promote the understanding of the specific pathway essential for floral regulation.

Genome-wide identification and expression analysis of the GSK gene family in Solanum tuberosum L. under abiotic stress and phytohormone treatments and functional characterization of StSK21 involvement in salt stress

Plant Glycogen Synthase Kinase 3 (GSK3)/SHAGGY-like kinase (GSK) proteins play important roles in modulating growth, development, and stress responses in several plant species. However, little is known about the members of the potato GSK (StGSK) family. Here, nine StGSK genes were identified and phylogenetically grouped into four clades. Gene duplication analysis revealed that segmental duplication contributed to the expansion of the StGSK family. Gene structure and motif pattern analyses indicated that similar exon/intron and motif organizations were found in StGSKs from the same clade. Conserved motif and kinase activity analyses indicated that the StGSKs encode active protein kinases, and they were shown to be distributed throughout whole cells. Cis-acting regulatory element analysis revealed the presence of many growth-, hormone-, and stress-responsive elements within the promoter regions of the StGSKs, which is consistent with their expression in different organs, and their altered expression in response to hormone and stress treatments. Association network analysis indicated that various proteins, including two confirmed BES1 family transcription factors, potentially interact with StGSKs. Overexpression of StSK21 provides enhanced sensitivity to salt stress in Arabidopsis thaliana plants. Overall, these results reveal that StGSK proteins are active protein kinases with purported functions in regulating growth, development, and stress responses.

Diversity, Function and Regulation of Cell Surface and Intracellular Immune Receptors in Solanaceae

The first layer of the plant immune system comprises plasma membrane-localized receptor proteins and intracellular receptors of the nucleotide-binding leucine-rich repeat protein superfamily. Together, these immune receptors act as a network of surveillance machines in recognizing extracellular and intracellular pathogen invasion-derived molecules, ranging from conserved structural epitopes to virulence-promoting effectors. Successful pathogen recognition leads to physiological and molecular changes in the host plants, which are critical for counteracting and defending against biotic attack. A breadth of significant insights and conceptual advances have been derived from decades of research in various model plant species regarding the structural complexity, functional diversity, and regulatory mechanisms of these plant immune receptors. In this article, we review the current state-of-the-art of how these host surveillance proteins function and how they are regulated. We will focus on the latest progress made in plant species belonging to the Solanaceae family, because of their tremendous importance as model organisms and agriculturally valuable crops.

Modification of Threonine-1050 of SlBRI1 regulates BR Signalling and increases fruit yield of tomato

BACKGROUND

Appropriate brassinosteroid (BR) signal strength caused by exogenous application or endogenous regulation of BR-related genes can increase crop yield. However, precise control of BR signals is difficult and can cause unstable effects and failure to reach full potential. Phosphorylated BRASSINOSTEROID INSENSITIVE1 (BRI1), the rate-limiting receptor in BR signalling, transduces BR signals, and we recently demonstrated that modifying BRI1 phosphorylation sites alters BR signal strength and botanical characteristics in Arabidopsis. However, the functions of such phosphorylation sites in agronomic characteristics of crops remain unclear.

RESULTS

In this work, we investigated the roles of tomato SlBRI1 threonine-1050 (Thr-1050). SlBRI1 mutant cu3^-abs1 plants expressing SlBRI1 with a non-phosphorylatable Thr-1050 (T1050A), with a wild-type SlBRI1 transformant used as a control, were examined. The results showed enhanced autophosphorylation of SlBRI1 and BR signal strength for cu3^-abs1 harbouring T1050A, which promoted yield through increased plant expansion, leaf area, fruit weight and fruit number per cluster but reduced nutrient contents, including ascorbic acid and soluble sugar levels. Moreover, plant height, stem diameter, and internodal distance were similar between the transgenic plants.

CONCLUSION

Our results reveal the biological role of Thr-1050 in tomato and provide a molecular basis for establishing high-yield crops by precisely controlling BR signal strength via phosphorylation site modification.