miR396 affects mycorrhization and root meristem activity in the legume Medicago truncatula

Abstract

These authors contributed equally to this work. SUMMARYThe root system is crucial for acquisition of resources from the soil. In legumes, the efficiency of mineral and water uptake by the roots may be reinforced due to establishment of symbiotic relationships with mycorrhizal fungi and interactions with soil rhizobia. Here, we investigated the role of miR396 in regulating the architecture of the root system and in symbiotic interactions in the model legume Medicago truncatula. Analyses with promoter-GUS fusions suggested that the mtr-miR396a and miR396b genes are highly expressed in root tips, preferentially in the transition zone, and display distinct expression profiles during lateral root and nodule development. Transgenic roots of composite plants that over-express the miR396b precursor showed lower expression of six growth-regulating factor genes (MtGRF) and two bHLH79-like target genes, as well as reduced growth and mycorrhizal associations. miR396 inactivation by mimicry caused contrasting tendencies, with increased target expression, higher root biomass and more efficient colonization by arbuscular mycorrhizal fungi. In contrast to MtbHLH79, repression of three GRF targets by RNA interference severely impaired root growth. Early activation of mtr-miR396b, concomitant with posttranscriptional repression of MtGRF5 expression, was also observed in response to exogenous brassinosteroids. Growth limitation in miR396 over-expressing roots correlated with a reduction in cell-cycle gene expression and the number of dividing cells in the root apical meristem. These results link the miR396 network to the regulation of root growth and mycorrhizal associations in plants.

An Atlas of Soybean Small RNAs Identifies Phased siRNAs from Hundreds of Coding Genes

“…As indicated in the table below, the predicted targets for all of the abundant phasiRNAs belong to a wide variety of transposable elements. The lower table lists phasiRNAs that are abundant and target 10 or more encoding a long-chain fatty acid CoA ligase (Table 2), functions in ROS scavenging (Bazin et al, 2013). The activity of these miRNAs to trigger phasiRNAs is consistent with complex posttranscriptional regulation in nodule development.…”

Transgenic Plants That Express the Phytoplasma Effector SAP11 Show Altered Phosphate Starvation and Defense Responses

“…By contrast, miR172, miR396, miR5020, miR5629, miR5645, and miR5648 showed significant down-regulation in the 35S::SAP11 AYWB transgenic plants. Among them, miR2111, miR399, and miR827 have been shown to be up-regulated by Pi starvation (Hsieh et al, 2009;Pant et al, 2009), and miR399 and miR827 play important roles in regulating Pi homeostasis (Liu et al, 2012;Huang et al, 2013;Lin et al, 2013); miR160 and miR396 are required for regulating the auxin signaling response and cell proliferation during leaf and root development (Gutierrez et al, 2009;Pulido and Laufs, 2010;Debernardi et al, 2012;Bazin et al, 2013); miR172 has been shown to regulate the transition from the vegetative to reproductive phases (Aukerman and Sakai, 2003;Wu et al, 2009); and miR394 is required for the regulation of leaf morphology and shoot meristem stem-cell maintenance (Song et al, 2012;Knauer et al, 2013). However, miR5020b, miR5629, miR5639, miR5645d, miR5648, miR5655, and miR850 are newly identified miRNAs with unknown functions.…”

The small RNA diversity from Medicago truncatula roots under biotic interactions evidences the environmental plasticity of the miRNAome

“…Analysis of the correlations between modules and responses to symbiotic or pathogenic microbes showed that the cyan and green modules appeared to be respectively negatively or positively correlated to the response to S. meliloti infection (r = -0.85 and r = 0.64) whereas the orange module grouped miRNAs discriminating symbiotic and pathogenic responses (r = 0.91). Again, certain miRNAs already known to be involved in the regulation of symbiotic and pathogenic processes, such as miR169 variants [20], miR171h and other variants [22,23], miR393 [16], miR396 [15], sly-miR482* and miR2118 [19], were found, suggesting coregulatory roles for the newly discovered miRNAs present in those modules. Interestingly, analysis of the enrichment of GO terms on target mRNAs (Additional file 6: Figure S9b), showed that miRNAs of the orange module (discriminating symbiotic and pathogenic responses) mainly target genes involved in defense response, proteolysis and nodule morphogenesis (23%, 23% and 12%, respectively).…”

“…In legumes, a role of miR399 in responses to increased phosphate, a nutritional status linked to effective mycorrhization, was reported by Branscheid et al [12]. Other miRNAs, like miR164, miR166 or miR396, were shown to play indirect roles in nodule development or mycorrhizal symbiosis due to their global impact on auxin responses and/or tissue patterning in roots [13][14][15]. Concerning plant-pathogen interactions, miRNAs linked to auxin signaling were related to defense reactions in A. thaliana [16,17] and more recent studies provided evidence that some miRNAs function as master regulators of diseaseresistance genes encoding nucleotide-binding site leucinerich repeat (NBS-LRR) proteins in diverse plants [18,19].…”