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Mitogen‐activated protein kinase (MPK) cascades play central signalling roles in plant immunity and stress response. The soybean orthologue of MPK kinase2 (GmMKK2) was recently identified as a potential signalling node whose expression is upregulated in the feeding site induced by soybean cyst nematode (SCN, Heterodera glycines). To investigate the role of GmMKK2 in soybean–SCN interactions, we overexpressed a catabolically inactive variant referred to as kinase‐dead variant (KD‐GmMKK2) using transgenic hairy roots. KD‐GmMKK2 overexpression caused significant reduction in soybean susceptibility to SCN, while overexpression of the wild‐type variant (WT‐GmMKK2) exhibited no effect on susceptibility. Transcriptome analysis indicated that KD‐GmMKK2 overexpressing plants are primed for SCN resistance via constitutive activation of defence signalling, particularly those related to chitin, respiratory burst, hydrogen peroxide and salicylic acid. Phosphoproteomic profiling of the WT‐GmMKK2 and KD‐GmMKK2 root samples upon SCN infection resulted in the identification of 391 potential targets of GmMKK2. These targets are involved in a broad range of biological processes, including defence signalling, vesicle fusion, chromatin remodelling and nuclear organization among others. Furthermore, GmMKK2 mediates phosphorylation of numerous transcriptional and translational regulators, pointing to the presence of signalling shortcuts besides the canonical MAPK cascades to initiate downstream signalling that eventually regulates gene expression and translation initiation. Finally, the functional requirement of specific phosphorylation sites for soybean response to SCN infection was validated by overexpressing phospho‐mimic and phospho‐dead variants of two differentially phosphorylated proteins SUN1 and IDD4. Together, our analyses identify GmMKK2 impacts on signalling modules that regulate soybean response to SCN infection. [ABSTRACT FROM AUTHOR]

We measured the speciation of dissolved Mn from the surface to just above the hydrothermal vents at 9°50′N East Pacific Rise in the open ocean of the Pacific over a 3‐week period. Total dissolved Mn concentrations ranged from 2.2 to 135 nmol L−1 with a significant contribution of dissolved Mn(III) bound to humic acid in one third of our samples representing up to 64% of the total dissolved Mn. These humic complexes were mostly detected in the hydrothermal vent plume and at the redox boundaries of the oxygen minimum zone in the water column. In the hydrothermal plume, the Mn(III)‐humic acid stabilized the manganese in solution up to a ~ 10,000‐fold dilution of the venting water. In the upper water column, Mn(III)‐humic acid was only detected after a squall and rain event, which indicates that it is a transient species, persistent over days to weeks. This temporal variability highlights the importance of non‐steady‐state processes in the open ocean, which may help to explain previous observations of a dissolved Mn maximum within oceanic oxygen minimum zones. [ABSTRACT FROM AUTHOR]

Soybean cyst nematode (SCN, Heterodera glycines ) is a serious root parasite of soybean ( Glycine max ) that induces extensive gene expression changes associated with pleiotropic biological activities in infected cells. However, the impacts of various SCN Hg Types on host transcriptome reprogramming remain largely unknown. Here, we developed and used two recombinant inbred lines (RIL-72 and RIL-137) to profile transcriptome reprogramming in the infection sites during the resistant and susceptible interactions with SCN Hg Type 1.2.5.7 and Type 0. SCN bioassays indicated that RIL-72 was susceptible to Type 1.2.5.7 but resistant to Type 0, whereas RIL-137 was resistant to both types. Comparative analysis of gene expression changes induced by Type 1.2.5.7 in the resistant and susceptible lines revealed distinct transcriptome regulation with a number of similarly and oppositely regulated genes. The expression levels of similarly regulated genes in the susceptible line appeared to be insufficient to mount an effective defense against SCN. The functional importance of oppositely regulated genes was confirmed using virus induced gene silencing and overexpression approaches. Further transcriptome comparisons revealed shared as well as Hg Type- and genotype-specific transcriptome reprogramming. Shared transcriptome responses were mediated through common SCN-responsive genes and conserved immune signaling, whereas genotype-specific responses were derived from genetic variability, metabolic and hormonal differences, and varied regulation of protein phosphorylation and ubiquitination. The conserved defense mechanisms together with genotype-specific responses would enable plants to trigger effective and tailored immune responses to various Hg types and adapt the defense response to their genetic backgrounds.

Root-knot nematodes ( Meloidogyne spp.) are widely spread root parasites that infect thousands of vascular plant species. These highly polyphagous nematodes engage in sophisticated interactions with host plants that results in the formation of knot-like structures known as galls whose ontogeny remains largely unknown. Here, we determined transcriptome changes and alternative splicing variants induced by Megalaima incognita in galls and neighboring root cells at two distinct infective stages. M. incognita induced substantial transcriptome changes in tomato roots both locally in galls and systemically in neighboring cells. A considerable parallel regulation of gene expression in galls and neighboring cells were detected, indicative of effective intercellular communications exemplified by suppression of basal defense responses particularly during the early stage of infection. The transcriptome analysis also revealed that M. incognita exerts a tight control over the cell cycle process as a whole that results in an increase of ploidy levels in the feeding sites and accelerated mitotic activity of the gall cells. Alternative splicing analysis indicated that M. incognita significantly modulates pre-mRNA splicing as a total of 9064 differentially spliced events from 2898 genes were identified where intron retention and exon skipping events were largely suppressed. Furthermore, a number of differentially spliced events were functionally validated using transgenic hairy root system and found to impact gall formation and nematode egg mass production. Together, our data provide unprecedented insights into the transcriptome and spliceome reprogramming induced by M. incognita in tomato with respect to gall ontogeny and nematode parasitism., Competing Interests: The authors declare no conflicts of interest., (© The Author(s) 2024. Published by Oxford University Press on behalf of Nanjing Agricultural University.)