Prospecting true ScYLV resistance in Saccharum hybrid parental population in India by symptom phenotyping and viral titre quantification

In sugarcane (Saccharum spp. hybrids) cultivation, viral diseases pose a great challenge across the globe. Yellow leaf (YL) disease is one of the important viral diseases caused by Sugarcane yellow leaf virus (ScYLV), a positive-sense ssRNA virus, genus Polerovirus, family Solemoviridae. The disease symptoms appear in later stages of crop growth during grand growth to maturity phase with intense midrib yellowing in the abaxial leaf surface. At present, this disease is managed through tissue (meristem) culture and healthy seed nurseries in India. However, the virus-free plants are infected quickly by secondary inoculum from aphid vectors in the field, which necessitates the importance of developing YL-resistant varieties. We screened about 600-625 sugarcane parental clones to identify true YL resistance based on 0-5 disease rating scale since 2015 and categorised them as resistant, moderately resistant, moderately susceptible, susceptible and highly susceptible. Leaf samples were collected from all these categories of plants during 2018-20 for the viral titre estimation through absolute quantification method (qRT-PCR assay). The viral load was invariably high in all categories of susceptible samples that ranged from 4.40 × 102 to 8.429 × 106, whereas in YL-free asymptomatic clones, the viral load ranged from 82.35 ± 5.90 to 5.121 × 104. The results clearly indicated that highest viral titre of 105-107 copies was present in all the susceptible clones irrespective of their disease severity grades. Our results clearly established that about 22.85% of apparently resistant sugarcane clones remained free from YL symptoms with significantly low ScYLV titre although we could not find a significant correlation between virus titre and symptom expression. The identified resistant parents will serve as sources of YL resistance to develop virus resistant sugarcane varieties.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03541-y.

Integrated structure-based protein interface prediction

Background

Identifying protein interfaces can inform how proteins interact with their binding partners, uncover the regulatory mechanisms that control biological functions and guide the development of novel therapeutic agents. A variety of computational approaches have been developed for predicting a protein’s interfacial residues from its known sequence and structure. Methods using the known three-dimensional structures of proteins can be template-based or template-free. Template-based methods have limited success in predicting interfaces when homologues with known complex structures are not available to use as templates. The prediction performance of template-free methods that only rely only upon proteins’ intrinsic properties is limited by the amount of biologically relevant features that can be included in an interface prediction model.

Results

We describe the development of an integrated method for protein interface prediction (ISPIP) to explore the hypothesis that the efficacy of a computational prediction method of protein binding sites can be enhanced by using a combination of methods that rely on orthogonal structure-based properties of a query protein, combining and balancing both template-free and template-based features. ISPIP is a method that integrates these approaches through simple linear or logistic regression models and more complex decision tree models. On a diverse test set of 156 query proteins, ISPIP outperforms each of its individual classifiers in identifying protein binding interfaces.

Conclusions

The integrated method captures the best performance of individual classifiers and delivers an improved interface prediction. The method is robust and performs well even when one of the individual classifiers performs poorly on a particular query protein. This work demonstrates that integrating orthogonal methods that depend on different structural properties of proteins performs better at interface prediction than any individual classifier alone.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12859-022-04852-2.

Differential host responses of sugarcane to Colletotrichum falcatum reveal activation of probable effector triggered immunity (ETI) in defence responses

KEY MESSAGE

The differential compatibility responses of sugarcane to Colletotrichum falcatum pathotypes depend on the nature of both host primary defence signalling cascades and pathogen virulence. The complex polyploidy of sugarcane genome and genetic variations in different cultivars of sugarcane remain a challenge to identify and characterise specific genes controlling the compatible and incompatible interactions between sugarcane and the red rot pathogen, Colletotrichum falcatum. To avoid host background variation in the interaction study, suppression subtractive hybridization (SSH)-based next-generation sequencing (NGS) technology was used in a sugarcane cultivar Co 7805 which is compatible with one C. falcatum pathotype but incompatible with another one. In the incompatible interaction (ICI-less virulent) 10,038 contigs were assembled from ~ 54,699,263 raw reads, while 4022 contigs were assembled from ~ 52,509,239 in the compatible interaction (CI-virulent). The transcripts homologous to CEBiP receptor and those involved in the signalling pathways of ROS, Ca²⁺, BR, and ABA were expressed in both interaction responses. In contrast, MAPK, ET, PI signalling pathways and JA amino conjugation related transcripts were found only in ICI. In temporal gene expression assays, 16 transcripts showed their highest induction in ICI than CI. Further, more than 17 transcripts specific to the pathogen were found only in CI, indicating that the pathogen colonizes the host tissue whereas it failed to do so in ICI. Overall, this study has identified for the first time that a probable PAMP triggered immunity (PTI) in both responses, while a more efficient effector triggered immunity (ETI) was found only in ICI. Moreover, pathogen proliferation could be predicted in CI based on transcript expression, which were homologous to Glomerella graminicola, the nearest clade to the perfect stage of C. falcatum (G. tucumanensis).

Carbohydrate active enzymes (CAZy) regulate cellulolytic and pectinolytic enzymes in Colletotrichum falcatum causing red rot in sugarcane

Colletotrichum falcatum, an ascomycete pathogen causes red rot of sugarcane which is specialized to infect cane stalks. Cellulolytic and pectinolytic enzymes are necessary for degradation of plant cell wall which stands as barrier for successful fungal pathogenesis. In the study, we have confined to the CAZy genes that regulate cellulolytic and pectinolytic enzymes in two distinctive pathotypes of C. falcatum. Comparative transcriptome analysis revealed that a number of CAZy genes producing cellulolytic and pectinolytic enzyme were present in the virulent (Cf671) and least virulent (RoC) pathotypes. Two consecutive transcriptome analyses (in vitro) were performed using Illumina Hi Seq 2500, further analysis was done with various bioinformatic tools. In vitro expression analysis of cutinase, glycoside hydrolyase and pectin-related genes revealed number of genes that attributes virulence. Numerous pectin-related genes involved in degradation of plant cell wall, pectinase and pectin lyase are considered to be key precursor in degradation of pectin in sugarcane. These results suggest that cellulolytic enzymes, cutinase and pectin-related genes are essential for degradation of sugarcane cell wall and considered to be an important pathogenic factor in C. falcatum. This is the first detailed report on sugarcane cell wall-degrading enzymes during its interaction with C. falcatum and also this comparative transcriptome analysis provided more insights into pathogen mechanism on C. falcatum.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-022-03113-6.

Role of miRNAs in the host-pathogen interaction between sugarcane and Colletotrichum falcatum, the red rot pathogen

KEY MESSAGE

Sugarcane microRNAs specifically involved during compatible and incompatible interactions with red rot pathogen Colletotrichum falcatum were identified. We have identified how the miRNAs regulate their gene targets and elaborated evidently on the underlying molecular mechanism of sugarcane defense response to C. falcatum for the first time. Resistance against the fungal pathogen Colletotrichum falcatum causing red rot is one of the most desirable traits for sustainable crop cultivation in sugarcane. To gain new insight into the host defense mechanism against C. falcatum, we studied the role of sugarcane microRNAs during compatible and incompatible interactions by adopting the NGS platform. We have sequenced a total of 80 miRNA families that comprised 980 miRNAs, and the putative targets of the miRNAs include transcription factors, membrane-bound proteins, glutamate receptor proteins, lignin biosynthesis proteins, signaling cascade proteins, transporter proteins, mitochondrial proteins, ER proteins, defense-related, stress response proteins, translational regulation proteins, cell proliferation, and ubiquitination proteins. Further, qRT-PCR analyses of 8 differentially regulated miRNAs and 26 gene transcript targets expression indicated that these miRNAs have a regulatory effect on the expression of respective target genes in most of the cases. Also, the results suggest that certain miRNA regulates many target genes that are involved in inciting early responses to the pathogen infection, signaling pathways, endoplasmic reticulum stress, and resistance gene activation through feedback response from various cellular processes during the compatible and incompatible interaction with the red rot pathogen C. falcatum. The present study revealed the role of sugarcane miRNAs and their target genes during sugarcane-C. falcatum interaction and provided new insight into the miRNA-mediated defense mechanism in sugarcane for the first time.

Selection of reference genes for normalization of microRNA expression in sugarcane stalks during its interaction with Colletotrichum falcatum

The microRNAs role in various cellular and metabolic functions is gaining more limelight in line with second-generation NGS technology. For the validation of candidate miRNA genes, the quantitative real-time PCR is the widely trusted and efficient method to follow. Sugarcane miRNAs are less explored in sugarcane defense response during their interaction with Colletotrichum falcatum inciting red rot. Further, for RT-qPCR experiments involving sugarcane miRNA expression studies, a stable internal reference gene is required. Hence, we have taken a study involving 20 candidate genes to identify stable expressing reference genes using NormFinder, geNorm, BestKeeper, and deltaCt statistical algorithms. The candidate reference genes included miRNAs and protein-coding genes. The results indicated that there is a variation in ranking among the algorithms. We found miR1862c as the stably expressed miRNA reference gene among the candidates and miR444b.2 along miR1862c formed the best reference gene pair combination, which can be used in the experiments aiming to explore sugarcane miRNAs in the defense mechanism against C. falcatum. The stable miRNA reference gene was further validated with other lesser stable reference gene candidates to assess the effect of stable reference genes during normalization. The present study evaluating the sugarcane miRNAs as reference genes for normalizing RT-qPCR expression data involving miRNAs during sugarcane × C. falcatum interaction is the first of its kind. Further, this systematic approach can be followed to assess the reference gene in various experimental conditions involving sugarcane miRNAs.

Development and characterization of genomic SSR marker for virulent strain-specific Colletotrichum falcatum infecting sugarcane

Colle totrichum falcatum, an intriguing pathogen causing red rot in sugarcane, exhibits enormous variation for pathogenicity under field conditions. A species-specific marker is very much needed to classify the virulence among the varying population and to identify the potential of a pathotype by mining the microsatellites, which are considered to be the largest genetic source to develop molecular markers for an organism. In this study, we have mined the C. falcatum genome using MISA database which yielded 12,121 SSRs from 48.1 Mb and 2745 SSRs containing sequences. The most frequent SSR types from the genome of C. falcatum was di-nucleotide which constitutes 50.89% followed by tri-nucleotide 39.60%, hepta-nucleotide 6.7%, hexa-nucleotide 1.38% and penta-nucleotide 1.3%. Over 90 SSR containing sequences from the genome were predicted using BlastX which are found to be non-homologs. Most of the annotated SSR containing sequences fell in CAZy superfamilies, proteases, peptidases, plant cell wall degrading enzymes (PCDWE) and membrane transporters which are considered to be pathogenicity gene clusters. Among them, glycosyl hydrolases (GH) were found to be abundant in SSR containing sequences which again proved our previous transcriptome results. Our in-silico results suggested that the mined microsatellites from C. falcatum genome show absence of homolog sequences which suggests that these markers could be used as an ideal species-specific molecular marker. Two virulence specific markers were characterized using conventional PCR assays from C. falcatum along with virulent species-specific (VSS) marker developed for C. gloeosporioides. The study lays the foundation for the development of C. falcatum specific molecular marker to phenotype the pathotypes based on virulence.

Normalized Mutual Information of phonetic sound to distinguish the speech of Parkinson's disease

This study has investigated the use of inter-personnel mutual information computed from the phonetic sound recordings to differentiate between Parkinson's disease (PD) and control subjects. The normalized mutual information (NMI) denotes the amount of information shared between the voice recordings of people within the same group: PD and Control. The hypothesis of this study was that within group NMI will be significantly different when compared with inter- group NMI. For each phonetic sound, the NMI was computed for every pairing of recordings for both the PD and control groups. Pearson correlation coefficient analysis was used to determine the association of NMI with clinical parameters including Unified Parkinson's Disease Rating Scale (UPDRS), Montreal cognitive assessment (MoCA) and disease duration. ANOVA test for the three phonetic sounds of control and PD subjects showed that there is significant difference between the intra-group mean NMI for the two groups (p <; 0.003) and also showed significant association with the UPDRS motor examination score, MoCA and disease duration.

Proteomic analysis of a compatible interaction between sugarcane and Sporisorium scitamineum

Smut caused by Sporisorium scitamineum is one of the important diseases of sugarcane with global significance. Despite the intriguing nature of sugarcane, S. scitamineum interaction, several pertinent aspects remain unexplored. This study investigates the proteome level alterations occurring in the meristem of a S. scitamineum infected susceptible sugarcane cultivar at whip emergence stage. Differentially abundant proteins were identified by 2DE coupled with MALDI-TOF/TOF-MS. Comprehensively, 53 sugarcane proteins identified were related to defence, stress, metabolism, protein folding, energy, and cell division; in addition, a putative effector of S. scitamineum, chorismate mutase, was identified. Transcript expression vis-à-vis the activity of phenylalanine ammonia lyase was relatively higher in the infected meristem. Abundance of seven candidate proteins in 2D gel profiles was in correlation with its corresponding transcript expression levels as validated by qRT-PCR. Furthermore, this study has opened up new perspectives on the interaction between sugarcane and S. scitamineum.

Quantification of sugarcane yellow leaf virus in sugarcane following transmission through aphid vector, Melanaphis sacchari

Yellow leaf caused by Sugarcane yellow leaf virus (SCYLV) is a serious constraint to sugarcane production in India and currently the disease epidemics occur on many of the susceptible varieties under field conditions. Studies were conducted on the virus transmission by sugarcane aphid Melanaphis sacchari in sugarcane by inoculating virus-free meristem derived from micro- propagated plants of sugarcane cv Co 86032 with viruliferous aphids. Virus transmission was confirmed through RT-PCR assays and subsequently SCYLV population was established through RT-qPCR. A maximum of 22.3 × 10(3), 3.16 × 10(6) and 4.78 × 10(6) copies of SCYLV-RNA targets were recorded in the plants after 7, 180 and 300 days, respectively. This study showed that the aphid species M. sacchari acts as an effective vector of SCYLV. The relative standard curve method in RT-qPCR efficiently detected the increment in SCYLV copy numbers in sugarcane following transmission through M. sacchari.

Differential regulation of defense-related gene expression in response to red rot pathogen Colletotrichum falcatum infection in sugarcane

Red rot is a serious disease of sugarcane caused by the fungus Colletotrichum falcatum imposing a considerable economic loss annually in all sugarcane-producing countries. In this study, we analyzed the early resistance response of sugarcane to red rot fungus by comparing the differences between control and inoculated stalk tissues. Differential display reverse transcription polymerase chain reaction (DD-RT-PCR) was employed to identify altered expression of genes in disease-resistant cv Co 93009, in response to pathogen infection. DD-RT-PCR identified 300 differentially expressed transcripts of which 112 were selected for further analysis. Cloning and sequence analysis of the isolated cDNA fragments resulted in functional categorization of these clones into five categories, of which the defense/stress/signaling group was the largest, with clones homologous to genes known to be actively involved in various pathogenesis-related functions in plant species. This group showed overexpression of several transcripts related to ethylene-mediated and jasmonic acid pathway of plant defense mechanisms. Of the 112 expressed sequence tags, validation of expression was carried out for five important genes whose role in plant defense mechanisms is well established. This is the first report of Colletotrichum-mediated gene regulation in sugarcane which has provided a set of candidate genes for detailed molecular dissection of signaling and defense responses in tropical sugarcane during the onset of red rot resistance.

Genetic diversity of Sugarcane bacilliform virus isolates infecting Saccharum spp. in India

Sugarcane bacilliform virus (SCBV), which causes leaf freckle in sugarcane, is a member of the genus Badnavirus. Studies were conducted to characterize SCBV in Saccharum officinarum germplasm and cultivated varieties in India by sequencing the complete genomes of five isolates. Genome lengths ranged from 7,553 to 7,884 nucleotides. Duplications in ORF3 and insertions in the RNase H-domain in some of the isolates were found to contribute to the large size of their genomes. The Indian SCBV isolates share identities of 69-85 % for the complete genomic sequence, indicating wide genetic diversity among them, and share 70-82 % identity with Sugarcane bacilliform Ireng Maleng virus (SCBIMV) and Sugarcane bacilliform Morocco virus (SCBMV), as well as 43-46 % identity with Banana streak virus (BSV) and BSV-related SCBV species from Guadeloupe, indicating that the Indian SCBV isolates are distinct from SCBV isolates reported to date. Irrespective of the region compared, SCBV isolates from India, Australia, and Morocco clustered together. BSV and BSV-related SCBV isolates from Guadeloupe formed another cluster. A phylogenetic analysis based on the partial RT/RNase H-sequence separated SCBV and BSV-related SCBV sequences into 11 SCBV groups viz. SCBV-A to -K. Among the 11 groups, the SCBV sequences separated under H, I, J, and K are newly identified in this study, representing three new species and are tentatively named as SCBBBV, SCBBOV, and SCBBRV. Thus, the PASC and phylogenetic analyses evidenced that the symptoms associated with badnaviruses in sugarcane in India are caused by at least three new species, SCBBBV, SCBBOV, and SCBBRV, besides SCBIMV and SCBMV represented by SCBV-BT and SCBV-Iscam, respectively.

Molecular characterization of Indian sugarcane streak mosaic virus isolate

Sugarcane streak mosaic virus (SCSMV), a member of the genus Poacevirus, family Potyviridae, is an important viral pathogen affecting sugarcane cultivation in India. The complete nucleotide sequence of a SCSMV isolate from India (SCSMV-IND) was determined. The linear, assembled, single-stranded positive-sense RNA genome of SCSMV-IND was 9,786 nucleotides in length (excluding the poly (A) tail) and encoded a polyprotein of 3,131 amino acid residues. The genome of SCSMV-IND shared high degree of sequence identity with SCSMV-PAK (93 % at nucleotide and 97 % at amino acid), and shared only 81 % nucleotide and 94 % amino acid identities with all the four SCSMV isolates (SCSMV-JP1, -JP2, -ID, and -THA). Phylogenetic tree analysis of the complete genome sequences of SCSMV isolates revealed that they can be clustered into two groups. SCSMV-IND and -AP isolates showed 18 % (nucleotide) divergence within the highly conserved 3' partial genome, suggesting a high level of genetic diversity among the Indian SCSMV isolates.