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1. The antagonistic MYB paralogs RH1 and RH2 govern anthocyanin leaf markings in Medicago truncatula

   https://doi.org/10.1111/nph.17097  

   Wang, Chongnan ; Ji, Wenkai ; Liu, Yucheng ; Zhou, Peng ; Meng, Yingying ; Zhang, Pengcheng ; Wen, Jiangqi ; Mysore, Kirankumar S. ; Zhai, Jixian ; Young, Nevin D. ; et al ( December 2020 , New Phytologist)

   Patterned leaf coloration in plants generates remarkable diversity in nature, but the underlying mechanisms remain largely unclear.

   Here, usingMedicago truncatulaleaf marking as a model, we show that the classicM. truncatulaleaf anthocyanin spot trait depends on two R2R3 MYB paralogous regulators, RED HEART1 (RH1) and RH2.

   RH1 mainly functions as an anthocyanin biosynthesis activator that specifically determines leaf marking formation depending on its C‐terminal activation motif. RH1 physically interacts with theM. truncatulabHLH protein MtTT8 and the WDR family member MtWD40‐1, and this interaction facilitates RH1 function in leaf anthocyanin marking formation. RH2 has lost transcriptional activation activity, due to a divergent C‐terminal domain, but retains the ability to interact with the same partners, MtTT8 and MtWD40‐1, as RH1, thereby acting as a competitor in the regulatory complex and exerting opposite effects. Moreover, our results demonstrate that RH1 can activate its own expression and that RH2‐mediated competition can repressRH1expression.

   Our findings reveal the molecular mechanism of the antagonistic gene paralogs RH1 and RH2 in determining anthocyanin leaf markings inM. truncatula, providing a multidimensional paralogous–antagonistic regulatory paradigm for fine‐tuning patterned pigmentation.

    

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2. Roles of very long-chain fatty acids in compound leaf patterning in Medicago truncatula

   https://doi.org/10.1093/plphys/kiad006  

   Wang, Hongfeng ; Lu, Zhichao ; Xu, Yiteng ; Zhang, Jing ; Han, Lu ; Chai, Maofeng ; Wang, Zeng-Yu ; Yang, Xianpeng ; Lu, Shiyou ; Tong, Jianhua ; et al ( January 2023 , Plant Physiology)

   Plant cuticles are composed of hydrophobic cuticular waxes and cutin. Very long-chain fatty acids (VLCFAs) are components of epidermal waxes and the plasma membrane and are involved in organ morphogenesis. By screening a barrelclover (Medicago truncatula) mutant population tagged by the transposable element of tobacco (Nicotiana tabacum) cell type1 (Tnt1), we identified two types of mutants with unopened flower phenotypes, named unopened flower1 (uof1) and uof2. Both UOF1 and UOF2 encode enzymes that are involved in the biosynthesis of VLCFAs and cuticular wax. Comparative analysis of the mutants indicated that the mutation in UOF1, but not UOF2, leads to the increased number of leaflets in M. truncatula. UOF1 was specifically expressed in the outermost cell layer (L1) of the shoot apical meristem (SAM) and leaf primordia. The uof1 mutants displayed defects in VLCFA-mediated plasma membrane integrity, resulting in the disordered localization of the PIN-FORMED1 (PIN1) ortholog SMOOTH LEAF MARGIN1 (SLM1) in M. truncatula. Our work demonstrates that the UOF1-mediated biosynthesis of VLCFAs in L1 is critical for compound leaf patterning, which is associated with the polarization of the auxin efflux carrier in M. truncatula.

    

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3. Genome‐wide methylation landscape during somatic embryogenesis in Medicago truncatula reveals correlation between Tnt1 retrotransposition and hyperactive methylation regions

   https://doi.org/10.1111/tpj.16744  

   Nandety, Raja Sekhar ; Oh, Sunhee ; Lee, Hee‐Kyung ; Krom, Nick ; Gupta, Rajeev ; Mysore, Kirankumar S. ( April 2024 , The Plant Journal)

   Medicago truncatulais a model legume for fundamental research on legume biology and symbiotic nitrogen fixation.Tnt1, a retrotransposon from tobacco, was used to generate insertion mutants inM. truncatulaR108. Approximately 21 000 insertion lines have been generated and publicly available.Tnt1retro‐transposition event occurs during somatic embryogenesis (SE), a pivotal process that triggers massive methylation changes. We studied the SE ofM. truncatulaR108 using leaf explants and explored the dynamic shifts in the methylation landscape from leaf explants to callus formation and finally embryogenesis. Higher cytosine methylation in all three contexts of CG, CHG, and CHH patterns was observed during SE compared to the controls. Higher methylation patterns were observed in assumed promoter regions (~2‐kb upstream regions of transcription start site) of the genes, while lowest was recorded in the untranslated regions. Differentially methylated promoter region analysis showed a higher CHH methylation in embryogenesis tissue samples when compared to CG and CHG methylation. Strong correlation (89.71%) was identified between the differentially methylated regions (DMRs) and the site ofTnt1insertions inM. truncatulaR108 and stronger hypermethylation of genes correlated with higher number ofTnt1insertions in all contexts of CG, CHG, and CHH methylation. Gene ontology enrichment and KEGG pathway enrichment analysis identified genes and pathways enriched in the signal peptide processing, ATP hydrolysis, RNA polymerase activity, transport, secondary metabolites, and nitrogen metabolism pathways. Combined gene expression analysis and methylation profiling showed an inverse relationship between methylation in the DMRs (regions spanning genes) and the expression of genes. Our results show that a dynamic shift in methylation happens during the SE process in the context of CG, CHH and CHG methylation, and theTnt1retrotransposition correlates with the hyperactive methylation regions.

    

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4. Lateral Leaflet Suppression 1 ( LLS1 ), encoding the MtYUCCA1 protein, regulates lateral leaflet development in Medicago truncatula

   https://doi.org/10.1111/nph.16539  

   Zhao, Baolin ; He, Liangliang ; Jiang, Chuan ; Liu, Ye ; He, Hua ; Bai, Quanzi ; Zhou, Shaoli ; Zheng, Xiaoling ; Wen, Jiangqi ; Mysore, Kirankumar S. ; et al ( April 2020 , New Phytologist)

   In species with compound leaves, the positions of leaflet primordium initiation are associated with local peaks of auxin accumulation. However, the role of auxin during the late developmental stages and outgrowth of compound leaves remains largely unknown.

   Using genome resequencing approaches, we identified insertion sites at four alleles of theLATERAL LEAFLET SUPPRESSION1(LLS1) gene, encoding the auxin biosynthetic enzyme YUCCA1 inMedicago truncatula.

   Linkage analysis and complementation tests showed that thells1mutant phenotypes were caused by theTnt1insertions that disrupted theLLS1gene. The transcripts ofLLS1can be detected in primordia at early stages of leaf initiation and later in the basal regions of leaflets, and finally in vein tissues at late leaf developmental stages. Vein numbers and auxin content are reduced in thells1‐1mutant. Analysis of thells1 sgl1andlls1 palm1double mutants revealed thatSGL1is epistatic toLLS1, andLLS1works withPALM1in an independent pathway to regulate the growth of lateral leaflets.

   Our work demonstrates that the YUCCA1/YUCCA4 subgroup plays very important roles in the outgrowth of lateral leaflets during compound leaf development ofM. truncatula, in addition to leaf venation.

    

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5. Genomic evidence of genetic variation with pleiotropic effects on caterpillar fitness and plant traits in a model legume

   https://doi.org/10.1111/mec.15113  

   Gompert, Zachariah ; Brady, Megan ; Chalyavi, Farzaneh ; Saley, Tara C. ; Philbin, Casey S. ; Tucker, Matthew J. ; Forister, Matthew L. ; Lucas, Lauren K. ( June 2019 , Molecular Ecology)

   Plant–insect interactions are ubiquitous, and have been studied intensely because of their relevance to damage and pollination in agricultural plants, and to the ecology and evolution of biodiversity. Variation within species can affect the outcome of these interactions. Specific genes and chemicals that mediate these interactions have been identified, but genome‐ or metabolome‐scale studies might be necessary to better understand the ecological and evolutionary consequences of intraspecific variation for plant–insect interactions. Here, we present such a study. Specifically, we assess the consequences of genome‐wide genetic variation in the model plantMedicago truncatulaforLycaeides melissacaterpillar growth and survival (larval performance). Using a rearing experiment and a whole‐genome SNP data set (>5 million SNPs), we found that polygenic variation inM. truncatulaexplains 9%–41% of the observed variation in caterpillar growth and survival. Genetic correlations among caterpillar performance and other plant traits, including structural defences and some anonymous chemical features, suggest that multipleM. truncatulaalleles have pleiotropic effects on plant traits and caterpillar performance (or that substantial linkage disequilibrium exists among distinct loci affecting subsets of these traits). A moderate proportion of the genetic effect ofM. truncatulaalleles onL. melissaperformance can be explained by the effect of these alleles on the plant traits we measured, especially leaf toughness. Taken together, our results show that intraspecific genetic variation inM. truncatulahas a substantial effect on the successful development ofL. melissacaterpillars (i.e., on a plant–insect interaction), and further point toward traits potentially mediating this genetic effect.

    

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