Despite of important functions of strigolactones (SLs) and karrikins (KARs) in plant development, plant–parasite and plant–fungi interactions, their roles in soybean–rhizobia interaction remain elusive. SL/KAR signaling genes
- Award ID(s):
- 1734145
- PAR ID:
- 10355389
- Date Published:
- Journal Name:
- Frontiers in Plant Science
- Volume:
- 13
- ISSN:
- 1664-462X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Summary GmMAX2a, GmD14s, andGmKAIs are activated by rhizobia infection. GmMAX2a restoredatmax2 root hair defects and soybean root hairs were changed inGmMAX2a overexpression (GmMAX2a ‐OE ) or knockdown (GmMAX2a ‐KD ) mutants.GmMAX2a ‐KD gave fewer, whereasGmMAX2a ‐OE produced more nodules than GUS hairy roots. Mutation ofGmMAX2a in itsKD orOE transgenic hairy roots affected the rhizobia infection‐induced increases in early nodulation gene expression. Both mutant hairy roots also displayed the altered auxin, jasmonate and abscisic acid levels, as further verified by transcriptomic analyses of their synthetic genes. Overexpression of an auxin synthetic geneGmYUC2a also affected SL and KAR signaling genes. GmMAX2a physically interacted with SL/KAR receptors GmD14s, GmKAIs, and GmD14Ls with different binding affinities, depending on variations in the critical amino acids, forming active D14/KAI‐SCFMAX2complexes. The knockdown mutant roots of the nodule‐specifically expressingGmKAI s andGmD14L s gave fewer nodules, with altered expression of several early nodulation genes. The expression levels ofGmKAI s, andGmD14L s were markedly changed inGmMAX2a mutant roots, so did their target repressor genesGmD53 s andGmSMAX1 s. Thus, SL and KAR signaling were involved in soybean–rhizobia interaction and nodulation partly through interactions with hormones, and this may explain the different effects of MXA2 orthologs on legume determinate and indeterminate nodulation. The study provides fresh insights into the roles of GmMAX2‐mediated SL/KAR signaling in soybean root hair and nodule formation. -
Abstract In the
Medicago truncatula-Sinorhizobium meliloti symbiosis, chemical signaling initiates rhizobial infection of root nodule tissue, where a large portion of the bacteria are endocytosed into root nodule cells to function in nitrogen-fixing organelles. These intracellular bacteria are subjected to an arsenal of plant-derived nodule-specific cysteine-rich (NCR) peptides, which induce the physiological changes that accompany nitrogen fixation. NCR peptides drive these intracellular bacteria toward terminal differentiation. The bacterial peptidase HrrP was previously shown to degrade host-derived NCR peptides and give the bacterial symbionts greater fitness at the expense of host fitness. ThehrrP gene is found in roughly 10% ofSinorhizobium isolates, as it is carried on an accessory plasmid. The objective of the present study is to identify peptidase genes in the core genome ofS. meliloti that modulate symbiotic outcome in a manner similar to the accessoryhrrP gene. In an overexpression screen of annotated peptidase genes, we identified one such symbiosis-associated peptidase (sap ) gene,sapA (SMc00451). When overexpressed,sapA leads to a significant decrease in plant fitness. Its promoter is active in root nodules, with only weak expression evident under free-living conditions. The SapA enzyme can degrade a broad range of NCR peptides in vitro. -
Summary Symbiotic nitrogen fixation in legumes is mediated by an interplay of signaling processes between plant hosts and rhizobial symbionts. In legumes, several secreted protein families have undergone expansions and play key roles in nodulation. Thus, identifying lineage‐specific expansions (
LSE s) of nodulation‐associated genes can be a strategy to discover candidate gene families.Using bioinformatic tools, we identified 13
LSE s of nodulation‐related secreted protein families, each unique to eitherGlycine ,Arachis orMedicago lineages. In theMedicago lineage, nodule‐specific Polycystin‐1, Lipoxygenase, Alpha Toxin (PLAT ) domain proteins (NPD s) expanded to five members. We examinedNPD function usingCRISPR /Cas9 multiplex genome editing to createMedicago truncatula knockout lines, targeting one to fiveNPD genes.NPD Mutant lines with differing combinations of
gene inactivations had progressively smaller nodules, earlier onset of nodule senescence, or ineffective nodules compared to the wild‐type control. Double‐ and triple‐knockout lines showed dissimilar nodulation phenotypes but coincided in upregulation of aNPD DHHC ‐type zinc finger and an aspartyl protease gene, possible candidates for the observed disturbance of proper nodule function.By postulating that gene family expansions can be used to detect candidate genes, we identified a family of nodule‐specific
PLAT domain proteins and confirmed that they play a role in successful nodule formation. -
Abstract Legumes, such as peas, beans, and alfalfa, have evolved a remarkable ability to establish root nodule symbioses with nitrogen-fixing soil bacteria to fulfill their nitrogen needs. This partnership is characterized by a high degree of specificity, occurring both within and between host and bacterial species. Consequently, nodulation capacity and nitrogen-fixing efficiency vary significantly among different plant–bacteria pairs. The genetic and molecular mechanisms regulating symbiotic specificity are diverse, involving a wide array of host and bacterial genes and signals with various modes of action. Understanding the genetic basis of symbiotic specificity could enable the development of strategies to enhance nodulation capacity and nitrogen fixation efficiency. This knowledge will also help overcome the host range barrier, which is a critical step toward extending root nodule symbiosis to non-leguminous plants. In this review, we provide an update on our current understanding of the genetics and evolution of recognition specificity in root nodule symbioses, providing more comprehensive insights into the molecular signaling in plant–bacterial interactions.
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null (Ed.)Nitrogen is a major determinant of plant growth and productivity and the ability of legumes to form a symbiotic relationship with nitrogen-fixing rhizobia bacteria allows legumes to exploit nitrogen-poor niches in the biosphere. But hosting nitrogen-fixing bacteria comes with a metabolic cost, and the process requires regulation. The symbiosis is regulated through three signal transduction pathways: in response to available nitrogen, at the initiation of contact between the organisms, and during the development of the nodules that will host the rhizobia. Here we provide an overview of our knowledge of how the three signaling pathways operate in space and time, and what we know about the cross-talk between symbiotic signaling for nodule initiation and organogenesis, nitrate dependent signaling, and autoregulation of nodulation. Identification of common components and points of intersection suggest directions for research on the fine-tuning of the plant’s response to rhizobia.more » « less