Faculty Opinions recommendation of A putative transporter is essential for integrating nutrient and hormone signaling with lateral root growth and nodule development in Medicago truncatula.

Medicago truncatula contains a family of at least five genes related to AUX1 of Arabidopsis thaliana (termed MtLAX genes for Medicago truncatula-like AUX1 genes). The high sequence similarity between the encoded proteins and AUX1 implies that the MtLAX genes encode auxin import carriers. The MtLAX genes are expressed in roots and other organs, suggesting that they play pleiotropic roles related to auxin uptake. In primary roots, the MtLAX genes are expressed preferentially in the root tips, particularly in the provascular bundles and root caps. During lateral root and nodule development, the genes are expressed in the primordia, particularly in cells that were probably derived from the pericycle. At slightly later stages, the genes are expressed in the regions of the developing organs where the vasculature arises (central position for lateral roots and peripheral region for nodules). These results are consistent with MtLAX being involved in local auxin transport and suggest that auxin is required at two common stages of lateral root and nodule development: development of the primordia and differentiation of the vasculature.

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The Medicago truncatula nodule identity gene MtNOOT1 is required for coordinated apical-basal development of the root

BMC Plant Biology ◽

10.1186/s12870-019-2194-z ◽

2019 ◽

Vol 19 (1) ◽

Cited By ~ 1

Author(s):

Defeng Shen ◽

Olga Kulikova ◽

Kerstin Guhl ◽

Henk Franssen ◽

Wouter Kohlen ◽

...

Keyword(s):

Cell Differentiation ◽

Medicago Truncatula ◽

Root Development ◽

Lateral Root ◽

Apical Meristem ◽

Spatial Development ◽

Root Apical Meristem ◽

Nodule Development ◽

Lateral Root Development ◽

Xylem Cell

Abstract Background Legumes can utilize atmospheric nitrogen by hosting nitrogen-fixing bacteria in special lateral root organs, called nodules. Legume nodules have a unique ontology, despite similarities in the gene networks controlling nodule and lateral root development. It has been shown that Medicago truncatula NODULE ROOT1 (MtNOOT1) is required for the maintenance of nodule identity, preventing the conversion to lateral root development. MtNOOT1 and its orthologs in other plant species -collectively called the NOOT-BOP-COCH-LIKE (NBCL) family- specify boundary formation in various aerial organs. However, MtNOOT1 is not only expressed in nodules and aerial organs, but also in developing roots, where its function remains elusive. Results We show that Mtnoot1 mutant seedlings display accelerated root elongation due to an enlarged root apical meristem. Also, Mtnoot1 mutant roots are thinner than wild-type and are delayed in xylem cell differentiation. We provide molecular evidence that the affected spatial development of Mtnoot1 mutant roots correlates with delayed induction of genes involved in xylem cell differentiation. This coincides with a basipetal shift of the root zone that is susceptible to rhizobium-secreted symbiotic signal molecules. Conclusions Our data show that MtNOOT1 regulates the size of the root apical meristem and vascular differentiation. Our data demonstrate that MtNOOT1 not only functions as a homeotic gene in nodule development but also coordinates the spatial development of the root.

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The Medicago truncatula PIN2 auxin transporter mediates basipetal auxin transport but is not necessary for nodulation

Journal of Experimental Botany ◽

10.1093/jxb/erz510 ◽

2019 ◽

Vol 71 (4) ◽

pp. 1562-1573 ◽

Cited By ~ 2

Author(s):

Jason L P Ng ◽

Astrid Welvaert ◽

Jiangqi Wen ◽

Rujin Chen ◽

Ulrike Mathesius

Keyword(s):

Medicago Truncatula ◽

Lateral Root ◽

Auxin Transport ◽

Nodule Development ◽

Moderate Increase ◽

Loss Of Function ◽

Auxin Response ◽

Root Numbers ◽

Auxin Transporter ◽

Basipetal Auxin Transport

Abstract The development of root nodules leads to an increased auxin response in early nodule primordia, which is mediated by changes in acropetal auxin transport in some legumes. Here, we investigated the role of root basipetal auxin transport during nodulation. Rhizobia inoculation significantly increased basipetal auxin transport in both Medicago truncatula and Lotus japonicus. In M. truncatula, this increase was dependent on functional Nod factor signalling through NFP, NIN, and NSP2, as well as ethylene signalling through SKL. To test whether increased basipetal auxin transport is required for nodulation, we examined a loss-of-function mutant of the M. truncatula PIN2 gene. The Mtpin2 mutant exhibited a reduction in basipetal auxin transport and an agravitropic phenotype. Inoculation of Mtpin2 roots with rhizobia still led to a moderate increase in basipetal auxin transport, but the mutant nodulated normally. No clear differences in auxin response were observed during nodule development. Interestingly, inoculation of wild-type roots increased lateral root numbers, whereas inoculation of Mtpin2 mutants resulted in reduced lateral root numbers compared with uninoculated roots. We conclude that the MtPIN2 auxin transporter is involved in basipetal auxin transport, that its function is not essential for nodulation, but that it plays an important role in the control of lateral root development.

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Auxin Response Factor 2 (ARF2), ARF3, and ARF4 Mediate Both Lateral Root and Nitrogen Fixing Nodule Development in Medicago truncatula

Frontiers in Plant Science ◽

10.3389/fpls.2021.659061 ◽

2021 ◽

Vol 12 ◽

Author(s):

Cristina Kirolinko ◽

Karen Hobecker ◽

Jiangqi Wen ◽

Kirankumar S. Mysore ◽

Andreas Niebel ◽

...

Keyword(s):

Medicago Truncatula ◽

Root Development ◽

Lateral Root ◽

Lateral Roots ◽

Nodule Development ◽

Nodule Formation ◽

Mrna Levels ◽

Nitrogen Fixing ◽

Auxin Response ◽

Small Interference Rna

Auxin Response Factors (ARFs) constitute a large family of transcription factors that mediate auxin-regulated developmental programs in plants. ARF2, ARF3, and ARF4 are post-transcriptionally regulated by the microRNA390 (miR390)/trans-acting small interference RNA 3 (TAS3) module through the action of TAS3-derived trans-acting small interfering RNAs (ta-siRNA). We have previously reported that constitutive activation of the miR390/TAS3 pathway promotes elongation of lateral roots but impairs nodule organogenesis and infection by rhizobia during the nitrogen-fixing symbiosis established between Medicago truncatula and its partner Sinorhizobium meliloti. However, the involvement of the targets of the miR390/TAS3 pathway, i.e., MtARF2, MtARF3, MtARF4a, and MtARF4b, in root development and establishment of the nitrogen-fixing symbiosis remained unexplored. Here, promoter:reporter fusions showed that expression of both MtARF3 and MtARF4a was associated with lateral root development; however, only the MtARF4a promoter was active in developing nodules. In addition, up-regulation of MtARF2, MtARF3, and MtARF4a/b in response to rhizobia depends on Nod Factor perception. We provide evidence that simultaneous knockdown of MtARF2, MtARF3, MtARF4a, and MtARF4b or mutation in MtARF4a impaired nodule formation, and reduced initiation and progression of infection events. Silencing of MtARF2, MtARF3, MtARF4a, and MtARF4b altered mRNA levels of the early nodulation gene nodulation signaling pathway 2 (MtNSP2). In addition, roots with reduced levels of MtARF2, MtARF3, MtARF4a, and MtARF4b, as well as arf4a mutant plants exhibited altered root architecture, causing a reduction in primary and lateral root length, but increasing lateral root density. Taken together, our results suggest that these ARF members are common key players of the morphogenetic programs that control root development and the formation of nitrogen-fixing nodules.

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Overexpression of miR160 affects root growth and nitrogen-fixing nodule number in Medicago truncatula

Functional Plant Biology ◽

10.1071/fp13123 ◽

2013 ◽

Vol 40 (12) ◽

pp. 1208 ◽

Cited By ~ 43

Author(s):

Pilar Bustos-Sanmamed ◽

Guohong Mao ◽

Ying Deng ◽

Morgane Elouet ◽

Ghazanfar Abbas Khan ◽

...

Keyword(s):

Root Growth ◽

Medicago Truncatula ◽

Expression Profiles ◽

Nodule Development ◽

Auxin Response ◽

Symbiotic Interaction ◽

Nodule Number ◽

Race Pcr ◽

Regulatory Loop

Auxin action is mediated by a complex signalling pathway involving transcription factors of the auxin response factor (ARF) family. In Arabidopsis, microRNA160 (miR160) negatively regulates three ARF genes (ARF10/ARF16/ARF17) and therefore controls several developmental processes, including primary and lateral root growth. Here, we analysed the role of miR160 in root development and nodulation in Medicago truncatula Gaertn. Bioinformatic analyses identified two main mtr-miR160 variants (mtr-miR160abde and mtr-miR160c) and 17 predicted ARF targets. The miR160-dependent cleavage of four predicted targets in roots was confirmed by analysis of parallel analysis of RNA ends (PARE) data and RACE-PCR experiments. Promoter-GUS analyses for mtr-miR160d and mtr-miR160c genes revealed overlapping but distinct expression profiles during root and nodule development. In addition, the early miR160 activation in roots during symbiotic interaction was not observed in mutants of the nodulation signalling or autoregulation pathways. Composite plants that overexpressed mtr-miR160a under two different promoters exhibited distinct defects in root growth and nodulation: the p35S:miR160a construct led to reduced root length associated to a severe disorganisation of the RAM, whereas pCsVMV:miR160a roots showed gravitropism defects and lower nodule numbers. Our results suggest that a regulatory loop involving miR160/ARFs governs root and nodule organogenesis in M. truncatula.

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Faculty Opinions recommendation of A nuclear factor Y interacting protein of the GRAS family is required for nodule organogenesis, infection thread progression, and lateral root growth.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.718238812.793493594 ◽

2014 ◽

Author(s):

Giles Oldroyd

Keyword(s):

Root Growth ◽

Lateral Root ◽

Infection Thread ◽

Nuclear Factor ◽

Interacting Protein ◽

Gras Family ◽

Nuclear Factor Y

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Faculty Opinions recommendation of Reprogramming of DNA methylation is critical for nodule development in Medicago truncatula.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.726907399.793526713 ◽

2016 ◽

Author(s):

Ton Bisseling

Keyword(s):

Dna Methylation ◽

Medicago Truncatula ◽

Nodule Development

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High throughput phenotyping of root growth dynamics, lateral root formation, root architecture and root hair development enabled by PlaRoM

Functional Plant Biology ◽

10.1071/fp09167 ◽

2009 ◽

Vol 36 (11) ◽

pp. 938 ◽

Cited By ~ 48

Author(s):

Nima Yazdanbakhsh ◽

Joachim Fisahn

Keyword(s):

Root Growth ◽

Growth Kinetics ◽

Lateral Root ◽

Root Architecture ◽

Imaging Techniques ◽

Plant Root ◽

Primary Root ◽

Growth Media ◽

Root Extension ◽

Lateral Root Development

Plant organ phenotyping by non-invasive video imaging techniques provides a powerful tool to assess physiological traits and biomass production. We describe here a range of applications of a recently developed plant root monitoring platform (PlaRoM). PlaRoM consists of an imaging platform and a root extension profiling software application. This platform has been developed for multi parallel recordings of root growth phenotypes of up to 50 individual seedlings over several days, with high spatial and temporal resolution. PlaRoM can investigate root extension profiles of different genotypes in various growth conditions (e.g. light protocol, temperature, growth media). In particular, we present primary root growth kinetics that was collected over several days. Furthermore, addition of 0.01% sucrose to the growth medium provided sufficient carbohydrates to maintain reduced growth rates in extended nights. Further analysis of records obtained from the imaging platform revealed that lateral root development exhibits similar growth kinetics to the primary root, but that root hairs develop in a faster rate. The compatibility of PlaRoM with currently accessible software packages for studying root architecture will be discussed. We are aiming for a global application of our collected root images to analytical tools provided in remote locations.

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Effects of a Nod-factor-overproducing strain of Sinorhizobium meliloti on the expression of the ENOD40 gene in Melilotus alba

Canadian Journal of Botany ◽

10.1139/b02-076 ◽

2002 ◽

Vol 80 (9) ◽

pp. 907-915 ◽

Cited By ~ 6

Author(s):

Walter F Giordano ◽

Michelle R Lum ◽

Ann M Hirsch

Keyword(s):

Lateral Root ◽

Sinorhizobium Meliloti ◽

Cortical Cell ◽

Host Cells ◽

Nodule Development ◽

Nodule Formation ◽

Additional Increase ◽

Nod Factor ◽

Melilotus Alba ◽

Different Strains

We have initiated studies on the molecular biology and genetics of white sweetclover (Melilotus alba Desr.) and its responses to inoculation with the nitrogen-fixing symbiont Sinorhizobium meliloti. Early nodulin genes such as ENOD40 serve as markers for the transition from root to nodule development even before visible stages of nodule formation are evident. Using Northern blot analysis, we found that the ENOD40 gene was expressed within 6 h after inoculation with two different strains of S. meliloti, one of which overproduces symbiotic Nod factors. Inoculation with this strain resulted in an additional increase in ENOD40 gene expression over a typical wild-type S. meliloti strain. Moreover, the increase in mRNA brought about by the Nod-factor-overproducing strain 24 h after inoculation was correlated with lateral root formation by using whole-mount in situ hybridization to localize ENOD40 transcripts in lateral root meristems and by counting lateral root initiation sites. Cortical cell divisions were not detected. We also found that nodulation occurred more rapidly on white sweetclover in response to the Nod-factor-overproducing strain, but ultimately there was no difference in nodulation efficiency in terms of nodule number or the number of roots nodulated by the two strains. Also, the two strains could effectively co-colonize the host when inoculated together, although a few host cells were occupied by both strains.Key words: ENOD40, Nod factor, Melilotus, Sinorhizobium, symbiosis.

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