Phosphorylation of S344 in the calmodulin‐binding domain negatively affects CCaMK function during bacterial and fungal symbioses

Calcium and Ca²⁺/calmodulin‐dependent protein kinase (CCaMK) plays a critical role in the signaling pathway that establishes root nodule symbiosis and arbuscular mycorrhizal symbiosis. Calcium‐dependent autophosphorylation is central to the regulation of CCaMK, and this has been shown to promote calmodulin binding. Here, we report a regulatory mechanism of Medicago truncatula CCaMK (MtCCaMK) through autophosphorylation of S344 in the calmodulin‐binding/autoinhibitory domain. The phospho‐ablative mutation S344A did not have significant effect on its kinase activities, and supports root nodule symbiosis and arbuscular mycorrhizal symbiosis, indicating that phosphorylation at this position is not required for establishment of symbioses. The phospho‐mimic mutation S344D show drastically reduced calmodulin‐stimulated substrate phosphorylation, and this coincides with a compromised interaction with calmodulin and its interacting partner, IPD3. Functional complementation tests revealed that the S344D mutation blocked root nodule symbiosis and reduced the mycorrhizal association. Furthermore, S344D was shown to suppress the spontaneous nodulation associated with a gain‐of‐function mutant of MtCCaMK (T271A), revealing that phosphorylation at S344 of MtCCaMK is adequate for shutting down its activity, and is epistatic over previously identified T271 autophosphorylation. These results reveal a mechanism that enables CCaMK to ‘turn off’ its function through autophosphorylation.     

The origin of the serpentine endemic Minuartia laricifolia subsp. ophiolitica by vicariance and competitive exclusion

Serpentine soils harbour a unique flora that is rich in endemics. We examined the evolution of serpentine endemism in Minuartia laricifolia, which has two ecologically distinct subspecies with disjunct distributions: subsp. laricifolia on siliceous rocks in the western Alps and eastern Pyrenees and subsp. ophiolitica on serpentine in the northern Apennines. We analysed AFLPs and chloroplast sequences from 30 populations to examine their relationships and how their current distributions and ecologies were influenced by Quaternary climatic changes. Minuartia laricifolia was divided into four groups with a BAPS cluster analysis of the AFLP data, one group consisted only of subsp. ophiolitica, while three groups were found within subsp. laricifolia: Maritime Alps, north‐western Alps and central Alps. The same groups were recovered in a neighbour‐joining tree, although subsp. ophiolitica was nested within the Maritime Alps group of subsp. laricifolia. Subspecies ophiolitica contained three different chloroplast haplotypes, which were also found in the Maritime Alps group of subsp. laricifolia. Given its high genetic diversity, subsp. ophiolitica appears to have arisen from subsp. laricifolia by vicariance instead of by long‐distance dispersal. Genetic and geographic evidence point to the Maritime Alps populations of subsp. laricifolia as the closest relatives of subsp. ophiolitica. We hypothesize that M. laricifolia was also able to grow on nonserpentine rocks in the northern Apennines during glacial periods when the vegetation was more open, but that only the serpentine‐adapted populations were able to persist until the present due to their competitive exclusion from more favourable habitats.     

Draft genome sequence of Streptomyces sp. strain Wigar10, isolated from a surface-sterilized garlic bulb

Streptomyces sp. strain Wigar10 was isolated from a surface-sterilized garlic bulb (Allium sativum var. Purple Stripe). Its genome encodes several novel secondary metabolite biosynthetic gene clusters and provides a genetic basis for further investigation of this strain's chemical biology and potential for interaction with its garlic host.     

Lotus japonicus symRK-14 uncouples the cortical and epidermal symbiotic program

SYMRK is a leucine-rich-repeat (LRR)-receptor kinase that mediates intracellular symbioses of legumes with rhizobia and arbuscular mycorrhizal fungi. It participates in signalling events that lead to epidermal calcium spiking, an early cellular response that is typically considered as central for intracellular accommodation and nodule organogenesis. Here, we describe the Lotus japonicus symRK-14 mutation that alters a conserved GDPC amino-acid sequence in the SYMRK extracellular domain. Normal infection of the epidermis by fungal or bacterial symbionts was aborted in symRK-14. Likewise, epidermal responses of symRK-14 to bacterial signalling, including calcium spiking, NIN gene expression and infection thread formation, were significantly reduced. In contrast, no major negative effects on the formation of nodule primordia and cortical infection were detected. Cumulatively, our data show that the symRK-14 mutation uncouples the epidermal and cortical symbiotic program, while indicating that the SYMRK extracellular domain participates in transduction of non-equivalent signalling events. The GDPC sequence was found to be highly conserved in LRR-receptor kinases in legumes and non-legumes, including the evolutionarily distant bryophytes. Conservation of the GDPC sequence in nearly one-fourth of LRR-receptor-like kinases in the genome of Arabidopsis thaliana suggests, however, that this sequence might also play an important non-symbiotic function in this plant.     

Loss of Progesterone Receptor-Mediated Actions Induce Preterm Cellular and Structural Remodeling of the Cervix and Premature Birth

A decline in serum progesterone or antagonism of progesterone receptor function results in preterm labor and birth. Whether characteristics of premature remodeling of the cervix after antiprogestins or ovariectomy are similar to that at term was the focus of the present study. Groups of pregnant rats were treated with vehicle, a progesterone receptor antagonist (onapristone or mifepristone), or ovariectomized on day 17 postbreeding. As expected, controls given vehicle delivered at term while rats delivered preterm after progesterone receptor antagonist treatment or ovariectomy. Similar to the cervix before term, the preterm cervix of progesterone receptor antagonist-treated rats was characterized by reduced cell nuclei density, decreased collagen content and structure, as well as a greater presence of macrophages per unit area. Thus, loss of nuclear progesterone receptor-mediated actions promoted structural remodeling of the cervix, increased census of resident macrophages, and preterm birth much like that found in the cervix at term. In contrast to the progesterone receptor antagonist-induced advance in characteristics associated with remodeling, ovariectomy-induced loss of systemic progesterone did not affect hypertrophy, extracellular collagen, or macrophage numbers in the cervix. Thus, the structure and macrophage census in the cervix appear sufficient for premature ripening and birth to occur well before term. With progesterone receptors predominantly localized on cells other than macrophages, the findings suggest that interactions between cells may facilitate the loss of progesterone receptor-mediated actions as part of a final common mechanism that remodels the cervix in certain etiologies of preterm and with parturition at term.