G protein regulation of disease resistance during infection of rice with rice blast fungus

Deciphering genetic factors contributing to enhanced resistance against Cercospora leaf blight in soybean (Glycine max L.) using GWAS analysis

Cercospora leaf blight (CLB), caused by Cercospora cf. flagellaris, C. kikuchii, and C. cf. sigesbeckiae, is a significant soybean [Glycine max (L.) Merr.] disease in regions with hot and humid conditions causing yield loss in the United States and Canada. There is limited information regarding resistant soybean cultivars, and there have been marginal efforts to identify the genomic regions underlying resistance to CLB. A Genome-Wide Association Study was conducted using a diverse panel of 460 soybean accessions from maturity groups III to VII to identify the genomic regions associated to the CLB disease. These accessions were evaluated for CLB in different regions of the southeastern United States over 3 years. In total, the study identified 99 Single Nucleotide Polymorphism (SNPs) associated with the disease severity and 85 SNPs associated with disease incidence. Across multiple environments, 47 disease severity SNPs and 23 incidence SNPs were common. Candidate genes within 10 kb of these SNPs were involved in biotic and abiotic stress pathways. This information will contribute to the development of resistant soybean germplasm. Further research is warranted to study the effect of pyramiding desirable genomic regions and investigate the role of identified genes in soybean CLB resistance.

QTL mapping and identification of candidate genes linked to red rot resistance in sugarcane

Sugarcane (Saccharum species hybrid) is one of the most important commercial crops cultivated worldwide for products like white sugar, bagasse, ethanol, etc. Red rot is a major sugarcane disease caused by a hemi-biotrophic fungus, Colletotrichum falcatum Went., which can potentially cause a reduction in yield up to 100%. Breeding for red rot-resistant sugarcane varieties has become cumbersome due to its complex genome and frequent generation of new pathotypes of red rot fungus. In the present study, a genetic linkage map was developed using a selfed population of a popular sugarcane variety CoS 96268. A QTL linked to red rot resistance (qREDROT) was identified, which explained 26% of the total phenotypic variation for the trait. A genotype-phenotype network analysis performed to account for epistatic interactions, identified the key markers involved in red rot resistance. The differential expression of the genes located in the genomic region between the two flanking markers of the qREDROT as well as in the vicinity of the markers identified through the genotype-phenotype network analysis in a set of contrasting genotypes for red rot infection further confirmed the mapping results. Further, the expression analysis revealed that the plant defense-related gene coding 26S protease regulatory subunit is strongly associated with the red rot resistance. The findings can help in the screening of disease resistant genotypes for developing red rot-resistant varieties of sugarcane.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03481-7.

Emerging themes in heterotrimeric G-protein signaling in plants

Heterotrimeric G-proteins are key signaling components involved during the regulation of a multitude of growth and developmental pathways in all eukaryotes. Although the core proteins (Gα, Gβ, Gγ subunits) and their basic biochemistries are conserved between plants and non-plant systems, seemingly different inherent properties of specific components, altered wirings of G-protein network architectures, and the presence of novel receptors and effector proteins make plant G-protein signaling mechanisms somewhat distinct from the well-established animal paradigm. G-protein research in plants is getting a lot of attention recently due to the emerging roles of these proteins in controlling many agronomically important traits. New findings on both canonical and novel G-protein components and their conserved and unique signaling mechanisms are expected to improve our understanding of this important module in affecting critical plant growth and development pathways and eventually their utilization to produce plants for the future needs. In this review, we briefly summarize what is currently known in plant G-protein research, describe new findings and how they are changing our perceptions of the field, and discuss important issues that still need to be addressed.

Heterotrimeric G-proteins facilitate resistance to plant pathogenic viruses in Arabidopsis thaliana (L.) Heynh

Heterotrimeric G-proteins, consisting of Gα, Gβ and Gγ subunits, are important signal transducers in eukaryotes. In plants, G-protein-mediated signaling contributes to defense against a range of fungal and bacterial pathogens. Here we studied response of G-protein-deficient mutants to ssRNA viruses representing 2 different families: Cucumber mosaic virus (CMV) (Bromoviridae) and Turnip mosaic virus (TuMV) (Potyviridae). We found that development of spreading necrosis on infected plants was suppressed in the Gβ-deficient mutant (agb1-2) compared to wild type and Gα-deficient mutant (gpa1-4). In accordance, ion leakage caused by viral infection was also significantly reduced in agb1-2 compared to wild type and gpa1-4. Nevertheless, both viruses replicated better in agb1-2 plants, while gpa1-4 was similar to wild type. Analysis of pathogenesis-related genes showed that Gβ negatively regulated salicylic acid, jasmonic acid and abscisic acid marker genes during CMV and TuMV infections. Interestingly, analysis of salicylic acid deficient transgenic plants indicated that salicylic acid did not affect resistance against these viruses and did not influence the Gβ-mediated defense response. We conclude that heterotrimeric G-proteins play a positive role in defense against viral pathogens probably by promoting cell death.

Deciphering Cis-Regulatory Element Mediated Combinatorial Regulation in Rice under Blast Infected Condition

Combinations of cis-regulatory elements (CREs) present at the promoters facilitate the binding of several transcription factors (TFs), thereby altering the consequent gene expressions. Due to the eminent complexity of the regulatory mechanism, the combinatorics of CRE-mediated transcriptional regulation has been elusive. In this work, we have developed a new methodology that quantifies the co-occurrence tendencies of CREs present in a set of promoter sequences; these co-occurrence scores are filtered in three consecutive steps to test their statistical significance; and the significantly co-occurring CRE pairs are presented as networks. These networks of co-occurring CREs are further transformed to derive higher order of regulatory combinatorics. We have further applied this methodology on the differentially up-regulated gene-sets of rice tissues under fungal (Magnaporthe) infected conditions to demonstrate how it helps to understand the CRE-mediated combinatorial gene regulation. Our analysis includes a wide spectrum of biologically important results. The CRE pairs having a strong tendency to co-occur often exhibit very similar joint distribution patterns at the promoters of rice. We couple the network approach with experimental results of plant gene regulation and defense mechanisms and find evidences of auto and cross regulation among TF families, cross-talk among multiple hormone signaling pathways, similarities and dissimilarities in regulatory combinatorics between different tissues, etc. Our analyses have pointed a highly distributed nature of the combinatorial gene regulation facilitating an efficient alteration in response to fungal attack. All together, our proposed methodology could be an important approach in understanding the combinatorial gene regulation. It can be further applied to unravel the tissue and/or condition specific combinatorial gene regulation in other eukaryotic systems with the availability of annotated genomic sequences and suitable experimental data.

Characterization of the heterotrimeric G-protein family and its transmembrane regulator from capsicum (Capsicum annuum L.)

Throughout evolution, organisms have created numerous mechanisms to sense and respond to their environment. One such highly conserved mechanism involves regulation by heterotrimeric G-protein complex comprised of alpha (Gα), beta (Gβ) and gamma (Gγ) subunits. In plants, these proteins play important roles in signal transduction pathways related to growth and development including response to biotic and abiotic stresses and consequently affect yield. In this work, we have identified and characterized the complete heterotrimeric G-protein repertoire in the Capsicum annuum (Capsicum) genome which consists of one Gα, one Gβ and three Gγ genes. We have also identified one RGS gene in the Capsicum genome that acts as a regulator of the G-protein signaling. Biochemical activities of the proteins were confirmed by assessing the GTP-binding and GTPase activity of the recombinant Gα protein and its regulation by the GTPase acceleration activity of the RGS protein. Interaction between different subunits was established using yeast- and plant-based analyses. Gene and protein expression profiles of specific G-protein components revealed interesting spatial and temporal regulation patterns, especially during root development and during fruit development and maturation. This research thus details the characterization of the first heterotrimeric G-protein family from a domesticated, commercially important vegetable crop.

Silencing of G proteins uncovers diversified plant responses when challenged by three elicitors in Nicotiana benthamiana

Signalling through heterotrimeric G protein composed of α-, β- and γ-subunits is essential in numerous physiological processes. Here we show that this prototypical G protein complex acts mechanistically by controlling elicitor sensitivity towards hypersensitive response (HR) and stomatal closure in Nicotiana benthamiana. Gα-, Gβ1-, and Gβ2-silenced plants were generated using virus-induced gene silencing. All silenced plants were treated with Xanthomonas oryzae harpin, Magnaporthe oryzae Nep1 and Phytophthora boehmeriae boehmerin, respectively. HR was dramatically impaired in Gα- and Gβ2-silenced plants treated with harpin, indicating that harpin-, rather than Nep1- or boehmerin-triggered HR, is Gα- and Gβ2-dependent. Moreover, all Gα-, Gβ1- and Gβ2-silenced plants significantly impaired elicitor-induced stomatal closure, elicitor-promoted nitric oxide (NO) production and active oxygen species accumulation in guard cells. To our knowledge, this is the first report of Gα and Gβ subunits involvement in stomatal closure in response to elicitors. Furthermore, silencing of Gα, Gβ1 and Gβ2 has an effect on the transcription of plant defence-related genes when challenged by three elicitors. In conclusion, silencing of G protein subunits results in many interesting plant cell responses, revealing that plant immunity systems employ both conserved and distinct G protein pathways to sense elicitors from distinct phytopathogens formed during plant-microbe evolution.

[A new rice dwarf1 mutant caused by a frame-shift mutation]

A dwarf mutant C6PS, which has the similar phenotype as the recessive mutant Dwarf1 (d1), was produced from tissue-cultured plants of Zhonghua 11. In its progeny (T2), the ratio of tall to dwarf plants was in agreement with the expected segregation ratio (3:1) of a single Mendelian inheritance gene, which indicated that the variation of plant height is caused by a single gene. To locate the mutation, C6PS was crossed with Zhenshan 97 and Mudanjiang 8 for producing two F2 populations of F2 (CM) and F2 (CZ), respectively. The plant height in each F2 population also showed the same segregation pattern as that in T2 generation. SSR marker RM430 closely linked to Dwarf1 was preferentially used to genotype the F2 (CZ) population because C6PS showed the similar phenotype to d1 mutant. RM430 was significantly associated with plant height, which indicated that the mutant gene might be D1. Comparative sequencing of D1 between C6PS and Zhonghua 11 showed a 6 bp deletion occurred in the splice site of its ninth exon. The marker C6PS-D1L/R designed on the 6 bp deletion was co-segregated with plant height in T2 generation. The results indicated that C6PS was a new mutant of D1. This mutation led to a 26 bp deletion of the transcript and resulted in a frame-shift mutation and a premature stop codon in C6PS, which could not translate the functional Gα protein. C6PS was weakly sensitive to Brassinolide based on the leaf inclination angle test.