Search

Heterotrimeric G proteins are important transducers of receptor signaling, functioning in plants with CLAVATA receptors in controlling shoot meristem size and with pathogen-associated molecular pattern receptors in basal immunity. However, whether specific members of the heterotrimeric complex potentiate cross-talk between development and defense, and the extent to which these functions are conserved across species, have not yet been addressed. Here we used CRISPR/Cas9 to knock out the maize G protein β subunit gene (Gβ) and found that the mutants are lethal, differing from those in Arabidopsis, in which homologous mutants have normal growth and fertility. We show that lethality is caused not by a specific developmental arrest, but by autoimmunity. We used a genetic diversity screen to suppress the lethal Gβ phenotype and also identified a maize Gβ allele with weak autoimmune responses but strong development phenotypes. Using these tools, we show that Gβ controls meristem size in maize, acting epistatically with G protein α subunit gene (Gα), suggesting that Gβ and Gα function in a common signaling complex. Furthermore, we used an association study to show that natural variation in Gβ influences maize kernel row number, an important agronomic trait. Our results demonstrate the dual role of Gβ in immunity and development in a cereal crop and suggest that it functions in cross-talk between these competing signaling networks. Therefore, modification of Gβ has the potential to optimize the trade-off between growth and defense signaling to improve agronomic production.

Reductions in growth and quality due to powdery mildew (PM) disease cause significant economic losses in tomato production. Oidium neolycopersici was identified as the fungal species responsible for tomato PM disease in South Korea in the present study, based on morphological and internal transcribed spacer DNA sequence analyses of PM samples collected from two remote regions (Muju and Miryang). The genes involved in resistance to this pathogen in the tomato accession 'KNU-12' (Solanum lycopersicum var. cerasiforme) were evaluated, and the inheritance of PM resistance in 'KNU-12' was found to be conferred via simple Mendelian inheritance of a mutant allele of the PM susceptibility locus Ol-2 (SlMlo1). Full-length cDNA analysis of this newly identified mutant allele (Slmlo1.1) showed that a 1-bp deletion in its coding region led to a frameshift mutation possibly resulting in SlMlo1 loss-of-function. An alternatively spliced transcript of Slmlo1.1 was observed in the cDNA sequences of 'KNU-12', but its direct influence on PM resistance is unclear. A derived cleaved amplified polymorphic sequence (dCAPS) and a high-resolution melting (HRM) marker were developed based on the 1-bp deletion in Slmlo1.1, and could be used for efficient marker-assisted selection (MAS) using 'KNU-12' as the source for durable and broad-spectrum resistance to PM. Key words: disease resistance, molecular marker, Oidium neolycopersici, powdery mildew, Solanum lycopersicum. Les diminutions de croissance et de qualite dues a l'oidium entraînent des pertes economiques importantes chez la tomate. Dans le present travail, l'Oidium neolycopersici a ete identifie comme etant l'espèce fongique responsable de l'oidium chez la tomate en Coree du Sud suite a l'etude de la morphologie et l'analyse des espaceurs internes transcrits chez une collection d'echantillons provenant de deux regions isolees (Muju et Miryang). Les gènes impliques dans la resistance a cet agent pathogène chez l'accession 'KNU-12' de la tomate (Solanum lycopersicum var. cerasiforme) ont ete evalues. L'heredite mendelienne de la resistance s'est averee être due a un allèle recessif au locus de susceptibilite Ol-2 (SlMlo1). Une analyse de l'ADNc complet de cet allèle mutant nouvellement identifie (Slmlo1.1) a revele une deletion d'un nucleotide dans la region codante, laquelle mène a un changement de cadre de lecture qui entraîne possiblement la perte de fonction de SlMlo1. Un variant d'epissage de Slmlo1.1 a ete observe au sein des sequences d'ADNc produites a partir de 'KNU-12', mais son effet sur la resistance a l'oidium reste incertain. Un marqueur dCAPS (<< derived cleaved amplified polymorphic sequence >>) et un marqueur HRM (<< high-resolution melting >>) ont ete mis au point sur la base de la deletion chez Slmlo1.1 et pourraient être employes en selection assistee au sein de croisements ou 'KNU-12' est employe comme source de resistance durable et a large spectre face a l'oidium. [Traduit par la Redaction] Mots-cles : resistance aux maladies, marqueur moleculaire, Oidium neolycopersici, oidium, Solanum lycopersicum., Introduction Powdery mildew (PM) disease is caused by obligate biotrophic ascomycete fungi belonging to the order Erysiphales. The major pathogens causing PM in tomato (Solanum lycopersicum) are Oidium spp. (O. [...]

Shoot growth depends on meristems, pools of stem cells that are maintained by a negative feedback loop between the CLAVATA pathway and the WUSCHEL homeobox gene (1). CLAVATA signalling involves a secreted peptide, CLAVATA3 (CLV3) (2), and its perception by cell surface leucine-rich repeat (LRR) receptors, including the CLV1 receptor kinase (3) and a LRR receptor-like protein, CLV2 (ref. 4). However, the signalling mechanisms downstream of these receptors are poorly understood, especially for LRR receptor-like proteins, which lack a signalling domain (5). Here we show that maize COMPACTPLANT2 (CT2) encodes the predicted α-subunit (Ga) of a heterotrimeric GTP binding protein. Maize ct2 phenotypes resemble Arabidopsis thaliana clavata mutants, and genetic, biochemical and functional assays indicate that CT2/Ga transmits a stem-cell-restrictive signal from a CLAVATA LRR receptor, suggesting a new function for Ga signalling in plants. Heterotrimeric GTP-binding proteins are membrane-associated molecular switches that are commonly activated by ligand binding to an associated sevenpass transmembrane (7TM) G-protein-coupled receptor (GPCR)(6). Recent studies have questioned the idea that plant heterotrimeric G proteins interact with canonical GPCRs (7), and our findings suggest that single pass transmembrane receptors act as GPCRs in plants, challenging the dogma that GPCRs are exclusively 7TM proteins., The ct2 reference allele (ct2-Ref) was obtained from the Maize Genetics Stock Center and introgressed into various inbred lines. It showed strong expressivity in B73, which we used for phenotypic [...]

The AMT1 family comprises major ammonium transporters in rice roots. In this study, we utilized AMT1 RNAi mutants (amt1) to explore how AMT1 affects NH4+- and NO3–-mediated morphological development and NH4+-responsive gene expression in roots. In the presence of NH4+, amt1 showed inhibition of NO3–- dependent lateral root development. The inhibitory action of NH4+ on lateral root growth was independent of the NO3– concentrations supplied to amt1 roots. The results of split root assays indicated that NH4+ exerts systemic action in inhibiting NO3–-dependent lateral root development in amt1. Further study with NAA and NOA, a potent auxin flux inhibitor, suggested that perturbation of membrane dynamics might not be the primary cause of the inhibitory action of NH4+ on NO3–-mediated lateral root growth in amt1 mutants. RNA-seq analysis of NH4+-responsive genes showed that approximately half of DEGs observed in wild-type roots were not detected in the DEGs of amt1 roots. Gene ontology enrichment analysis suggested that the expression of specific functional gene groups were affected by amt1 during the early response to NH4+. Auxin-responsive gene expression and root gravity responses were altered in amt1. This study demonstrated that AMT1 affects the interactions not only between ammonium and nitrate in lateral root growth but also between auxin and NH4+ in rice roots. [ABSTRACT FROM AUTHOR]