Jacalin lectin At5g28520 is regulated by ABA and miR846

Integrative Transcriptome, miRNAs, Degradome, and Phytohormone Analysis of Brassica rapa L. in Response to Plasmodiophora brassicae

Clubroot is an infectious root disease caused by Plasmodiophora brassicae in Brassica crops, which can cause immeasurable losses. We analyzed integrative transcriptome, small RNAs, degradome, and phytohormone comprehensively to explore the infection mechanism of P. brassicae. In this study, root samples of Brassica rapa resistant line material BrT24 (R-line) and susceptible line material Y510-9 (S-line) were collected at four different time points for cytological, transcriptome, miRNA, and degradome analyses. We found the critical period of disease resistance and infection were at 0-3 DAI (days after inoculation) and 9-20 DAI, respectively. Based on our finding, we further analyzed the data of 9 DAI vs. 20 DAI of S-line and predicted the key genes ARF8, NAC1, NAC4, TCP10, SPL14, REV, and AtHB, which were related to clubroot disease development and regulating disease resistance mechanisms. These genes are mainly related to auxin, cytokinin, jasmonic acid, and ethylene cycles. We proposed a regulatory model of plant hormones under the mRNA-miRNA regulation in the critical period of P. brassicae infection by using the present data of the integrative transcriptome, small RNAs, degradome, and phytohormone with our previously published results. Our integrative analysis provided new insights into the regulation relationship of miRNAs and plant hormones during the process of disease infection with P. brassicae.

Identification of Novel miRNAs and Their Target Genes in the Response to Abscisic Acid in Arabidopsis

miRNAs are involved in various biological processes, including adaptive responses to abiotic stress. To understand the role of miRNAs in the response to ABA, ABA-responsive miRNAs were identified by small RNA sequencing in wild-type Arabidopsis, as well as in abi1td, mkkk17, and mkkk18 mutants. We identified 10 novel miRNAs in WT after ABA treatment, while in abi1td, mkkk17, and mkkk18 mutants, three, seven, and nine known miRNAs, respectively, were differentially expressed after ABA treatment. One novel miRNA (miRn-8) was differentially expressed in the mkkk17 mutant. Potential target genes of the miRNA panel were identified using psRNATarget. Sequencing results were validated by quantitative RT-PCR of several known and novel miRNAs in all genotypes. Of the predicted targets of novel miRNAs, seven target genes of six novel miRNAs were further validated by 5' RLM-RACE. Gene ontology analyses showed the potential target genes of ABA-responsive known and novel miRNAs to be involved in diverse cellular processes in plants, including development and stomatal movement. These outcomes suggest that a number of the identified miRNAs have crucial roles in plant responses to environmental stress, as well as in plant development, and might have common regulatory roles in the core ABA signaling pathway.

Genome-wide identification and expression analysis of dirigent-jacalin genes from plant chimeric lectins in Moso bamboo (Phyllostachys edulis)

Dirigent-jacalin (D-J) genes belong to the plant chimeric lectin family, and play vital roles in plant growth and resistance to abiotic and biotic stresses. To explore the functions of the D-J family in the growth and development of Moso bamboo (Phyllostachys edulis), their physicochemical properties, phylogenetic relationships, gene and protein structures, and expression patterns were analyzed in detail. Four putative PeD-J genes were identified in the Moso bamboo genome, and microsynteny and phylogenetic analyses indicated that they represent a new branch in the evolution of plant lectins. PeD-J proteins were found to be composed of a dirigent domain and a jacalin-related lectin domain, each of which contained two different motifs. Multiple sequence alignment and homologous modeling analysis indicated that the three-dimensional structure of the PeD-J proteins was significantly different compared to other plant lectins, primarily due to the tandem dirigent and jacalin domains. We surveyed the upstream putative promoter regions of the PeD-Js and found that they mainly contained cis-acting elements related to hormone and abiotic stress response. An analysis of the expression patterns of root, leaf, rhizome and panicle revealed that four PeD-J genes were highly expressed in the panicle, indicating that they may be required during the formation and development of several different tissue types in Moso bamboo. Moreover, PeD-J genes were shown to be involved in the rapid growth and development of bamboo shoots. Quantitative Real-time PCR (qRT PCR) assays further verified that D-J family genes were responsive to hormones and stresses. The results of this study will help to elucidate the biological functions of PeD-Js during bamboo growth, development and stress response.

Bacillus amyloliquefaciens FZB42 represses plant miR846 to induce systemic resistance via a jasmonic acid-dependent signalling pathway

Bacillus amyloliquefaciens FZB42 is a type of plant growth-promoting rhizobacterium (PGPR) which activates induced systemic resistance (ISR) in Arabidopsis. Blocking of the synthesis of cyclic lipopeptides and 2,3-butanediol by FZB42, which have been demonstrated to be involved in the priming of ISR, results in the abolishment of the plant defence responses. To further clarify the ISR activated by PGPRs at the microRNA (miRNA) level, small RNA (sRNA) libraries from Arabidopsis leaves after root irrigation with FZB42, FZB42ΔsfpΔalsS and control were constructed and sequenced. After fold change selection, promoter analysis and target prediction, miR846-5p and miR846-3p from the same precursor were selected as candidate ISR-associated miRNAs. miR846 belongs to the non-conserved miRNAs, specifically exists in Arabidopsis and its function in the plant defence response remains unclear. The disease severity of transgenic Arabidopsis overexpressing miR846 (OEmiR846) or knockdown miR846 (STTM846) against Pseudomonas syringae DC3000 suggests that the miR846 expression level in Arabidopsis is negatively correlated with disease resistance. Moreover, miR846 in Arabidopsis Col-0 is repressed after methyl jasmonate treatment. In addition, jasmonic acid (JA) signalling-related genes are up-regulated in STTM846, and the stomatal apertures of STTM846 are also less than those in Arabidopsis Col-0 after methyl jasmonate treatment. Furthermore, the disease resistance of STTM846 transgenic Arabidopsis against Pseudomonas syringae pv. tomato DC3000 (Pst DC3000) is blocked by the addition of the JA biosynthetic inhibitor diethyldiethiocarbamic acid (DIECA). Taken together, our results suggest that B. amyloliquefaciens FZB42 inoculation suppresses miR846 expression to induce Arabidopsis systemic resistance via a JA-dependent signalling pathway.

Genome-Wide Analysis of MicroRNA Responses to the Phytohormone Abscisic Acid in Populus euphratica

MicroRNA (miRNA) is a type of non-coding small RNA with a regulatory function at the posttranscriptional level in plant growth development and in response to abiotic stress. Previous studies have not reported on miRNAs responses to the phytohormone abscisic acid (ABA) at a genome-wide level in Populus euphratica, a model tree for studying abiotic stress responses in woody plants. Here we analyzed the miRNA response to ABA at a genome-wide level in P. euphratica utilizing high-throughput sequencing. To systematically perform a genome-wide analysis of ABA-responsive miRNAs in P. euphratica, nine sRNA libraries derived from three groups (control, treated with ABA for 1 day and treated with ABA for 4 days) were constructed. Each group included three libraries from three individual plantlets as biological replicate. In total, 151 unique mature sequences belonging to 75 conserved miRNA families were identified, and 94 unique sequences were determined to be novel miRNAs, including 56 miRNAs with miRNA(*) sequences. In all, 31 conserved miRNAs and 31 novel miRNAs response to ABA significantly differed among the groups. In addition, 4132 target genes were predicted for the conserved and novel miRNAs. Confirmed by real-time qPCR, expression changes of miRNAs were inversely correlated with the expression profiles of their putative targets. The Populus special or novel miRNA-target interactions were predicted might be involved in some biological process related stress tolerance. Our analysis provides a comprehensive view of how P. euphratica miRNA respond to ABA, and moreover, different temporal dynamics were observed in different ABA-treated libraries.

AtRAV1 and AtRAV2 overexpression in cotton increases fiber length differentially under drought stress and delays flowering

There is a longstanding problem of an inverse relationship between cotton fiber qualities versus high yields. To better understand drought stress signaling and adaptation in cotton (Gossypium hirsutum) fiber development, we expressed the Arabidopsis transcription factors RELATED_TO_ABA-INSENSITIVE3/VIVIPAROUS1/(RAV1) and AtRAV2, which encode APETALA2-Basic3 domain proteins shown to repress transcription of FLOWERING_LOCUS_T (FT) and to promote stomatal opening cell-autonomously. In three years of field trials, we show that AtRAV1 and AtRAV2-overexpressing cotton had ∼5% significantly longer fibers with only marginal decreases in yields under well-watered or drought stress conditions that resulted in 40-60% yield penalties and 3-7% fiber length penalties in control plants. The longer transgenic fibers from drought-stressed transgenics could be spun into yarn which was measurably stronger and more uniform than that from well-watered control fibers. The transgenic AtRAV1 and AtRAV2 lines flowered later and retained bolls at higher nodes, which correlated with repression of endogenous GhFT-Like (FTL) transcript accumulation. Elevated expression early in development of ovules was observed for GhRAV2L, GhMYB25-Like (MYB25L) involved in fiber initiation, and GhMYB2 and GhMYB25 involved in fiber elongation. Altered expression of RAVs controlling critical nodes in developmental and environmental signaling hierarchies has the potential for phenotypic modification of crops.

Molecular characterization of Helja, an extracellular jacalin-related protein from Helianthus annuus: Insights into the relationship of this protein with unconventionally secreted lectins

Jacalin-related lectins (JRLs) encompass cytosolic, nuclear and vacuolar members displaying the jacalin domain in one or more copies or in combination with unrelated domains. Helianthus annuus jacalin (Helja) is a mannose-specific JRL previously identified in the apoplast of Helianthus annuus seedlings, and this protein has been proposed to follow unconventional secretion. Here, we describe the full-length Helja cDNA sequence, which presents a unique jacalin domain (merolectin) and the absence of a signal peptide, confirming that the protein cannot follow the classical ER-dependent secretory pathway. Helja mRNA is present in seeds, cotyledons, roots and hypocotyls, but no transcripts were detected in the leaves. Searches for sequence similarity showed that Helja is barely similar to other JRLs present in H. annuus databases and less than 45% identical to other monocot or dicot JRLs. Strikingly, most of the merolectins recovered through data mining using Helja as a query were predicted as apoplastic, although most of these proteins lack the signal peptide required for classical secretion. Thus, Helja is the first bait identified to recover putative unconventionally secreted lectins. Because the recovered JRLs are widely distributed among the plant kingdom, an as yet unknown role for jacalin lectins in the apoplast is emerging.

Small RNA profiling reveals regulation of Arabidopsis miR168 and heterochromatic siRNA415 in response to fungal elicitors

BACKGROUND

Small RNAs (sRNAs), including small interfering RNAs (siRNAs) and microRNAs (miRNAs), have emerged as important regulators of eukaryotic gene expression. In plants, miRNAs play critical roles in development, nutrient homeostasis and abiotic stress responses. Accumulating evidence also reveals that sRNAs are involved in plant immunity. Most studies on pathogen-regulated sRNAs have been conducted in Arabidopsis plants infected with the bacterial pathogen Pseudomonas syringae, or treated with the flagelin-derived elicitor peptide flg22 from P. syringae. This work investigates sRNAs that are regulated by elicitors from the fungus Fusarium oxysporum in Arabidopsis.

RESULTS

Microarray analysis revealed alterations on the accumulation of a set of sRNAs in response to elicitor treatment, including miRNAs and small RNA sequences derived from massively parallel signature sequencing. Among the elicitor-regulated miRNAs was miR168 which regulates ARGONAUTE1, the core component of the RNA-induced silencing complex involved in miRNA functioning. Promoter analysis in transgenic Arabidopsis plants revealed transcriptional activation of MIR168 by fungal elicitors. Furthermore, transgenic plants expressing a GFP-miR168 sensor gene confirmed that the elicitor-induced miR168 is active. MiR823, targeting Chromomethylase3 (CMT3) involved in RNA-directed DNA methylation (RdDM) was also found to be regulated by fungal elicitors. In addition to known miRNAs, microarray analysis allowed the identification of an elicitor-inducible small RNA that was incorrectly annotated as a miRNA. Studies on Arabidopsis mutants impaired in small RNA biogenesis demonstrated that this sRNA, is a heterochromatic-siRNA (hc-siRNA) named as siRNA415. Hc-siRNAs are known to be involved in RNA-directed DNA methylation (RdDM). SiRNA415 is detected in several plant species.

CONCLUSION

Results here presented support a transcriptional regulatory mechanism underlying MIR168 expression. This finding highlights the importance of miRNA functioning in adaptive processes of Arabidopsis plants to fungal infection. The results of this study also lay a foundation for the involvement of RdDM processes through the activity of siRNA415 and miR823 in mediating regulation of immune responses in Arabidopsis plants.