A wound-induced small polypeptide gene family is upregulated in soybean nodules

Wound-induced polypeptides improve resistance against Pseudomonas syringae pv. tomato DC3000 in Arabidopsis

Wound-induced polypeptides (WIPs) are a novel class of polypeptides with the length less than 100 amino acids. Our previous research has identified a number of WIP genes in soybean (Glycine max) root nodules. However, functions of WIPs in planta remains largely unknown. Here, we identified five WIP-encoding genes, AtWIP1-5, in Arabidopsis. Among them, AtWIP1 and -2 are ubiquitously expressed in a partially overlapping pattern as revealed by both qRT-PCR and promoter:GUS assays. Subcellular localization analyses reveal that both AtWIP1 and -2 are localized at the plasma membrane while AtWIP1 shows a punctate distribution pattern. AtWIP1, -2 are transcriptionally induced by flg22 treatment, but repressed by effector(s) of Pseudomonas syringae pv. tomato DC3000 (Pst DC3000). Heterologous overexpression of GmWIP genes enhances resistance of Arabidopsis to Pst DC3000 at the cost of growth inhibition. Moreover, overexpression of GmWIP genes promotes pattern-triggered immunity (PTI) evidenced by increased expressions of flg22-inducible genes and enhanced seedling growth inhibition under flg22 treatment. Taken together, our results indicate that WIPs positively regulate plant resistance against Pst DC3000 by enhancing PTI responses.

Examination of Endogenous Peptides in Medicago truncatula Using Mass Spectrometry Imaging

Plant science is an important, rapidly developing area of study. Within plant science, one area of study that has grown tremendously with recent technological advances, such as mass spectrometry, is the field of plant-omics; however, plant peptidomics is relatively underdeveloped in comparison with proteomics and metabolomics. Endogenous plant peptides can act as signaling molecules and have been shown to affect cell division, development, nodulation, reproduction, symbiotic associations, and defense reactions. There is a growing need to uncover the role of endogenous peptides on a molecular level. Mass spectrometric imaging (MSI) is a valuable tool for biological analyses as it allows for the detection of thousands of analytes in a single experiment and also displays spatial information for the detected analytes. Despite the prediction of a large number of plant peptides, their detection and imaging with spatial localization and chemical specificity is currently lacking. Here we analyzed the endogenous peptides and proteins in Medicago truncatula using matrix-assisted laser desorption/ionization (MALDI)-MSI. Hundreds of endogenous peptides and protein fragments were imaged, with interesting peptide spatial distribution changes observed between plants in different developmental stages.

NODULES WITH ACTIVATED DEFENSE 1 is required for maintenance of rhizobial endosymbiosis in Medicago truncatula

The symbiotic interaction between legume plants and rhizobia results in the formation of root nodules, in which symbiotic plant cells host and harbor thousands of nitrogen-fixing rhizobia. Here, a Medicago truncatula nodules with activated defense 1 (nad1) mutant was identified using reverse genetics methods. The mutant phenotype was characterized using cell and molecular biology approaches. An RNA-sequencing technique was used to analyze the transcriptomic reprogramming of nad1 mutant nodules. In the nad1 mutant plants, rhizobial infection and propagation in infection threads are normal, whereas rhizobia and their symbiotic plant cells become necrotic immediately after rhizobia are released from infection threads into symbiotic cells of nodules. Defense-associated responses were detected in nad1 nodules. NAD1 is specifically present in root nodule symbiosis plants with the exception of Morus notabilis, and the transcript is highly induced in nodules. NAD1 encodes a small uncharacterized protein with two predicted transmembrane helices and is localized at the endoplasmic reticulum. Our data demonstrate a positive role for NAD1 in the maintenance of rhizobial endosymbiosis during nodulation.

Small-peptide signals that control root nodule number, development, and symbiosis

Many legumes have the capacity to enter into a symbiotic association with soil bacteria generically called 'rhizobia' that results in the formation of new lateral organs on roots called nodules within which the rhizobia fix atmospheric nitrogen (N). Up to 200 million tonnes of N per annum is fixed by this association. Therefore, this symbiosis plays an integral role in the N cycle and is exploited in agriculture to support the sustainable fixation of N for cropping and animal production in developing and developed nations. Root nodulation is an expendable developmental process and competency for nodulation is coupled to low-N conditions. Both nodule initiation and development is suppressed under high-N conditions. Although root nodule formation enables sufficient N to be fixed for legumes to grow under N-deficient conditions, the carbon cost is high and nodule number is tightly regulated by local and systemic mechanisms. How legumes co-ordinate nodule formation with the other main organs of nutrient acquisition, lateral roots, is not fully understood. Independent mechanisms appear to regulate lateral roots and nodules under low- and high-N regimes. Recently, several signalling peptides have been implicated in the local and systemic regulation of nodule and lateral root formation. Other peptide classes control the symbiotic interaction of rhizobia with the host. This review focuses on the roles played by signalling peptides during the early stages of root nodule formation, in the control of nodule number, and in the establishment of symbiosis. Here, we highlight the latest findings and the gaps in our understanding of these processes.