Phospholipase Ds in plants: Their role in pathogenic and symbiotic interactions

A new bacterial phospholipase D with specificity for phosphatidylethanolamine over phosphatidylcholine

Phospholipases D (PLDs) are key enzymes involved in numerous processes in all living organisms. PLD catalyzes, notably, the hydrolysis of different phospholipids (PLs) generating phosphatidic acid (PA). PA is an important moiety at the crossroads of multiple metabolic pathways and it is involved in signaling reactions, cancer genesis in mammals, bacterial infections and the defense response in plants. In current study, searching for a plant-like PLD in microbes, a new PLD has been identified in the bacterium Dechloromonas aromatica RCB that had been previously isolated from polluted soil. Here we have recombinantly expressed and characterized this particular PLD which shares common enzymatic features with classical PLDs from plants and bacteria regarding pH and temperature. However, compared to these already known PLDs, this PLD from D. aromatica has a strong preference for phosphatidylethanolamine (PE) over all other PLs, especially phosphatidylcholine (PC). Moreover, we showed that this PLD has a typoselectivity for unsaturated PE that does not exist for PC. Interestingly, the recombinant expression of this new bacterial PLD led to a stunning change in PL composition and amount in E. coli, especially for PA. These findings offer new perspectives on PA production and regulation in bacteria.

An emerging role of heterotrimeric G-proteins in nodulation and nitrogen sensing

MAIN CONCLUSION

A comprehensive understanding of nitrogen signaling cascades involving heterotrimeric G-proteins and their putative receptors can assist in the production of nitrogen-efficient plants. Plants are immobile in nature, so they must endure abiotic stresses including nutrient stress. Plant development and agricultural productivity are frequently constrained by the restricted availability of nitrogen in the soil. Non-legume plants acquire nitrogen from the soil through root membrane-bound transporters. In depleted soil nitrogen conditions, legumes are naturally conditioned to fix atmospheric nitrogen with the aid of nodulation elicited by nitrogen-fixing bacteria. Moreover, apart from the symbiotic nitrogen fixation process, nitrogen uptake from the soil can also be a significant secondary source to satisfy the nitrogen requirements of legumes. Heterotrimeric G-proteins function as molecular switches to help plant cells relay diverse stimuli emanating from external stress conditions. They are comprised of Gα, Gβ and Gγ subunits, which cooperate with several downstream effectors to regulate multiple plant signaling events. In the present review, we concentrate on signaling mechanisms that regulate plant nitrogen nutrition. Our review highlights the potential of heterotrimeric G-proteins, together with their putative receptors, to assist the legume root nodule symbiosis (RNS) cascade, particularly during calcium spiking and nodulation. Additionally, the functions of heterotrimeric G-proteins in nitrogen acquisition by plant roots as well as in improving nitrogen use efficiency (NUE) have also been discussed. Future research oriented towards heterotrimeric G-proteins through genome editing tools can be a game changer in the enhancement of the nitrogen fixation process. This will foster the precise manipulation and production of plants to ensure global food security in an era of climate change by enhancing crop productivity and minimizing reliance on external inputs.

Major-effect quantitative trait locus qLKR4.1 encodes a phospholipase Dδ protein associated with low-K+ stress tolerance by promoting root length

qLKR4.1, controlling low K⁺ resistance in tomato, was fine-mapped to an interval of 67.5 kb on chromosome A04, and one gene encoding phospholipase Dδ was identified as a candidate gene. In plants, changes in root length are an important morphological response to low K⁺ (LK) stress; however, the underlying genetics in tomato remain unclear. Here, we combined bulked segregant analysis-based whole-genome sequencing, single-nucleotide polymorphism haplotyping, and fine genetic mapping to identify a candidate gene as a major-effect quantitative trait loci (QTL), i.e., qLKR4.1, which was associated with LK tolerance due to increased root elongation in the tomato line JZ34. Through multiple analyses, we found that Solyc04g082000 is the most likely candidate for qLKR4.1, which encodes phospholipase Dδ (PLDδ). Increased root elongation under LK in JZ34 may be attributed to a non-synonymous single-nucleotide polymorphism in the Ca²⁺-binding domain region of this gene. Solyc04g082000 increases root length through its PLDδ activity. Silencing of Solyc04g082000^Arg in JZ34 led to a significant decrease in root length compared with silencing of Solyc04g082000^His allele in JZ18 under LK conditions. Mutation of a Solyc04g082000 homologue in Arabidopsis, pldδ, resulted in decreased primary root lengths under LK conditions, compared to the wild type. Transgenic tomato expressing the qLKR4.1^Arg allele from JZ34 exhibited a significant increase in root length compared with the wild type expressing the allele from JZ18 under LK conditions. Taken together, our results confirm that the PLDδ gene Solyc04g082000 exerts important functions in increasing tomato root length and LK tolerance.

The captivating role of calcium in plant-microbe interaction

Plant immune response is fascinating due to the complete absence of a humoral system. The adaptive immune response in plants relies on the intracellular orchestration of signalling molecules or intermediates associated with transcriptional reprogramming. Plant disease response phenomena largely depend on pathogen recognition, signal perception, and intracellular signal transduction. The pathogens possess specific pathogen-associated molecular patterns (PAMP) or microbe-associated molecular patterns (MAMP), which are first identified by pattern recognition receptors (PRRs) of host plants for successful infection. After successful pathogen recognition, the defence response is initiated within plants. The first line of non-specific defence response is called PAMP-triggered immunity (PTI), followed by the specific robust signalling is called effector-triggered immunity (ETI). Calcium plays a crucial role in both PTI and ETI. The biphasic induction of reactive oxygen species (ROS) is inevitable in any plant-microbe interaction. Calcium ions play crucial roles in the initial oxidative burst and ROS induction. Different pathogens can induce calcium accumulation in the cytosol ([Ca²⁺]_Cyt), called calcium signatures. These calcium signatures further control the diverse defence-responsive proteins in the intracellular milieu. These calcium signatures then activate calcium-dependent protein kinases (CDPKs), calcium calmodulins (CaMs), calcineurin B-like proteins (CBLs), etc., to impart intricate defence signalling within the cell. Decoding this calcium ionic map is imperative to unveil any plant microbe interplay and modulate defence-responsive pathways. Hence, the present review is unique in developing concepts of calcium signature in plants and their subsequent decoding mechanism. This review also intends to articulate early sensing of calcium oscillation, signalling events, and comprehensive mechanistic roles of calcium within plants during pathogenic ingression. This will accumulate and summarize the exciting roles of calcium ions in plant immunity and provide the foundation for future research.

Innovation Research on Symbiotic Relationship of Organization’s Tacit Knowledge Transfer Network

The sustainable development of organizations is inseparable from innovation, and tacit knowledge is the core resource used to achieve organizational innovation. Due to the implicitness of tacit knowledge and the complexity of members’ relationships, symbiotic relationships between members have dramatically affected the transfer effect of tacit knowledge. However, previous studies on tacit knowledge transfer only focus on the characteristics of the subject or object; fewer consider the role of symbiotic relationships between knowledge subjects. An organization’s tacit knowledge transfer network (OTKTN) is a dynamic knowledge transfer network established among multiple members. Tacit knowledge transfer and sharing among network members conform to the symbiotic feature. To examine various relationships between members, and to investigate the mechanisms that impact tacit knowledge transfer, this article aims to analyze the symbiotic relationships in OTKTN based on the symbiotic perspective. The Lotka–Volterra model was used to construct symbiotic evolution model, and symbiotic coefficients were constructed from the four levels: knowledge-based psychological personal ownership (KPPO) of the knowledge provider, media richness, trust of the knowledge receiver, and organizational rewards matching, to discuss symbiotic modes. Finally, numerical simulation software was applied to simulate the evolution of knowledge levels in members. The results show that the four kinds of symbiotic modes between members include independence, commensalism, asymmetric mutualism, and symmetric mutualism. Symmetric mutualism is the best mode. In this mode, maximum level in independence mode affects the final stable knowledge level; the initial knowledge amount and natural growth rate both affect knowledge growth rate. Media richness, receiver’s trust, and organizational rewards matching can increase members’ tacit knowledge, but the knowledge provider’s KPPO inhibits members’ tacit knowledge growth. This article provides guidance to form a healthy symbiotic relationship and help organizations increase tacit knowledge.