Maize silk is the long thread-like strand of Zea mays plant material, which has been recognized in multiple benefits, including medicine and cosmetics, and is also known as a traditional Chinese medicine [54]. Perhaps, biotic factors, especially fungi, reduce crop yield production on the second level after insects. Some corn smut, Fusarium ear rot, Gibberella ear rot, brown spot etc., have been identified as major fungal diseases as well as mycotoxins production in maize plants [12, 24]. The previous study identified gene level expression that in Fusarium graminearum (Fg) infection conditions, more genes were influced compared to other Fusarium verticillioides (Fv), Trichoderma atroviride (Ta), and Ustilago maydis (Um) fungal infections silk of Zea mays[18]. In this study, we used these transcriptome data with different bioinformatics analysis tools (details in materials and methods) to analyze the expression profiles of the transcript isoform genes, alternative splicing, and lncRNAs and construct reciprocal interaction network with the target to significant transcript isoform, AS, of lncRNA and miRNA. Globally been reported about lncRNA work as precursors of miRNA to influence miRNA biosynthesis as well as interfere with the functions [55, 56], and alternatively, spliced and transcript isoform gene expression profiles have impact on the targets of miRNA during development, biotic and abiotic stress [57–59]. We identified 39651 and 34027 transcript isoform of genes, 3819 and 3320 alternative splicing significantly differentially expressed of control datasets A and B. In addition, 3212 lncRNAs have been identified, and 530 lncRNAs identified are significantly differentially expressed in multiple fungal infection conditions.
Transcript isoforms are generated from the same genes by alternative splicing events that produce phenotypes complexity and diversity of eukaryotes[60, 61]. In this study, we found 12568 transcript isoform genes(9502 genes), but 2409 genes of transcript isoform have never been identified in previous gene-level analyses (Fig. 6)[18]. For that analysis, transcript fragment was aligned to exons after than summed to a gene-level count table formerly differential gene expression analysis. Summarizing diverse transcript isoforms to the gene level ignores the dynamics of alternative splicing and may unclear transcript isoform-specific associations with phenotypes[19]. The enrichment analysis of this transcript isoform of genes, 17 of Um and 14 of Fg conditions downregulated transcript isoforms involved in the pyruvate metabolism pathway, in which genes ZM00001EB289570 have three transcript variants (isoform), that two variant involved Aldo-keto reductase family 4 member C9 proteins (EC:1.1.1.2), while transcript variant (ZM00001EB289570_T001) synthesis NADP-dependent oxidoreductase domain-containing protein (Fig. 7; Table S4). These pathways plays a key role in energy production through glycolysis to maintain cell metabolic homeostasis[62]. These transcript isoform expressions value influences under the different fungal infections in silk of Zea mays, that pyruvate dehydrogenase E2 components and pyruvate kinase down regulated in Ustilago maydis fungal infection infections, but in others infection not significant expression,[63] et al. have been identified upregulated in the glycolysis pathway Poa pratensis plants under cold treatments and also found in root tissue of wheat and rice abiotic stress conditions[64, 65]. The alcohol dehydrogenase proteins transcript isoform expression level was upregulated and downregulated in F. graminearum (Fg) other than did not have significant expression. Dihydrolipoamide dehydrogenase is an essential enzyme involved in various metabolic pathways [65] but in our study have down regulated in Fg infection conditions.
In different biotic and abiotic stresses, such as salinity [66], heat[67], cold[68], viruses[69], fungi[70], viruses, drought [71–74] and chemical deficiencies [75] have been identified that alternative splicing has a major impact on plant responses via genes and proteins enables produce protein isoforms with various functions, localizations, and regulatory features to react and adapt to particular biotic and abiotic stress conditions[76–78]. In this study, we identified the influence of AS events genes in the multiple fungal infected silks of Zea mays. Out of 712 genes, 570 differentially alternative splicing (DAS) genes were identified, and 142 AS events occurred with multiple splicing in the same genes (Fig. 2). The 305 AS splicing genes found only in AS, did not find previous gene levels[18] and transcript isoform genes (Fig. 6). Interestingly, out of them, the five genes ZM00001EB115220; U2AF, ZM00001EB356610: P68, ZM00001EB174130: SPF30, ZM00001EB283000: Prp38, ZM00001EB358100: hnRNPs involved in the spliceosome pathway in which three genes down regulated in both Fg and Um fungal infections conditions, and two genes up regulated in Fg fungal infection condition silk of Zea mays (Table S2B) with different AS events. [71] have found one gene involved in the spliceosome, the U2AF (U2 small nuclear ribonucleoprotein auxiliary factor), plays an important role in recognizing 3' splicing sites and binding to 3' AG intron border[79, 80] have proposed that U2AF35 gene expression level increased in flower but the root of Arabidopsis thaliana decreasing. [81] et al. found splicing factor 30(SPF30) in multiple plant species, mostly in rice and Arabidopsis thaliana, have variations of expression value. In this analysis, U2AF and SPF30 come under the ZM00001EB115220 and ZM00001EB174130 genes, which down regulated in Um fungal infections conditions, but others have no significant expressions. ZM00001EB358100: hnRNPs are RNA-binding proteins and play an important role in multiple aspects, including alternative splicing, nucleic acid, and translation regulations [82, 83]. These genes positively express in Fg infection of maize silk, but other conditions are not significant. 134 genes found in all segment means AS, alternative isoforms, and genes level (Fig. 6), the 21 genes were involved in the metabolic pathway, in which 14 genes present in the biosynthesis of secondary metabolites. The gene (Zm00001eb397190) have been identified five transcript isoforms, in which transcript isoform three (Zm00001eb397190_T003) involved in non-specific serine/threonine protein kinase, while others four transcript isoform participate in protein activated protein kinase, these proteins pay important role in mRNA cis splicing, via spliceosome biological process[84], in this study have been identified transcript isoform three upregulated in Fg and Um fungal infected samples out of five. In addition, have been saw that alternative slicing 5’ stop side (A5SS) as well as Exon skipping (ES) in Fg and Um fungal infected (Fig. 8).
Long noncoding RNAs (lncRNAs) can participate in and regulate numerous gene transcriptions, splicing, and nuclear structure of plants by acting in a trans site away from the transcription site and play significant roles in the biosynthesis and metabolism of secondary metabolites, development process, and stress response[85–87]. Through comparative analysis, out of 8805 lncRNAs, we identified 149 (see results) significantly expressed lncRNAs in multiple fungal-infected silks of Zea mays. Many researchers have identified in plants and animals that lncRNAs have the capacity to attached and modified their miRNAs after than inhibit its downstream functions[53, 56, 88, 89]; so we used 325 known miRNAs from miRbase database and found 389 interaction sites in 88 lncRNAs [90, 91]. miRNA and lncRNA are noncoding RNA, but both play important roles in regulating RNA splicing and gene expression[92]. [58] et al. have proposed that the miRNA and mRNA interactions work as inhibitors or promoters of anti-cancer drug resistance. Thus, miRNA and AS interaction is a potent target for eliciting drug resistance [93]. Some isoforms can avoid being targeted because they lack the miRNA binding site. In some circumstances, the miRNA binding site presence or absence in the isoform, influences the potential of its silence by a complementary miRNA[59]. [94] et al. have found lncRNA act as miRNA targets or decoys, involving gene expression regulations [56, 95–97]. In this study, we investigate the complex regulatory network of lncRNAs, miRNAs, alternative isoforms, and alternative splicing genes by Cytoscape (Fig. 4)[85], in which we found 389 interactions between lncRNAs and miRNAs, 331 cleavages and 58 translate site (Table S3A). The 9147-interaction site within 556 significant AS genes and 131 lncRNA (Table S3B). Out of 12568 significant alternative isoforms, 4144 alternative isoforms targeted 149 lncRNA and made interaction 460916 sites (Table S3C). Further, 103 common target genes between AS and alternative isoforms genes were found. In addition, uncovered functional divergence of lncRNAs targeted alternative isoforms and alternative splicing genes which are present in multiple biological process with the following GO terms: response to stimulus, cellular process, cellular component organization biogenesis, localization, metabolic process, positive regulation, signaling, rhythmic process, carbon utilization common target 103 genes, other than, development process, detoxification, growth process, multiple organismal process, negative of biological process, multi-organism process, and reproduction process, found in both target genes (Fig. 5), but cell proliferation, localization, biological regulation, immune system responses, and regulation of biological process found in only alternative isoform target involvements. Positive expression saw in Fv, Ta, Um infected samples of MSTRG.8680.2 lncRNA, interacted with zma-MIR159g, Zuma-miR166a, and zma-MIR169c miRNA; these ncRNA targeting protein kinase domain-containing protein alternative isoform (Zm00001eb077770_T001) which were expressed down-regulated in Fg, Um but these genes also found alternative 3' stop site in Fg infected samples, these protein phosphorylation play important roles in biotic stress, development of plants[98, 99]. MSTRG.4934.1 down regulated lncRNA in Fg, Ta, and Um infection conditions and targeted exonuclease domain-containing protein, NC domain-containing protein-related, Protein kinase superfamily protein, Integral membrane HPP family protein genes, which have the same influences in Fg and Um infections conditions, but NC domain-containing protein-related genes formed alternative splicing in 5' start side. However, significant express lncRNA and target MADS-box transcription factor 26 (Zm00001eb174000_T006), NAC transcription factor (Zm00001eb183190_T002), Myb family transcription factor PHL6 (Zm00001eb232000_T003), etc. (Table S6). Previous studies have shown that these transcription factors play key role in the flowering, ripening, and development of peanut and tomato [96, 100, 101]. The present study indicated that lncRNAs might play an important role in transcriptional and post-transcriptional levels by regulating non coding and transcription factors in fungal-infected silk of Zea mays.