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1. Glutaredoxin AtGRXS8 represses transcriptional and developmental responses to nitrate in Arabidopsis thaliana roots

   https://doi.org/10.1002/pld3.227  

   Ehrary, Ahmad; Rosas, Miguel; Carpinelli, Sophia; Davalos, Oscar; Cowling, Craig; Fernandez, Francisco; Escobar, Matthew; Baxter, ed., Ivan (June 2020, Plant Direct)

   Abstract Glutaredoxins (GRXs) are small oxidoreductase enzymes that can reduce disulfide bonds in target proteins. The class III GRX gene family is unique to land plants, andArabidopsis thalianahas 21 class III GRXs, which remain largely uncharacterized. About 80% ofA. thalianaclass III GRXs are transcriptionally regulated by nitrate, and several recent studies have suggested roles for these GRXs in nitrogen signaling. Our objective was to functionally characterize two nitrate‐induced GRX genes,AtGRXS5andAtGRXS8, defining their roles in signaling and development in theA. thalianaroot. We demonstrated thatAtGRXS5andAtGRXS8are primarily expressed in root and shoot vasculature (phloem), and that the corresponding GRX proteins display nucleo‐cytosolic subcellular localization. Ectopic expression ofAtGRXS8in transgenic plants caused major alterations in root system architecture: Normal primary root development, but a near absence of lateral roots. RNA sequencing demonstrated that the roots ofAtGRXS8‐overexpressing plants show strongly reduced transcript abundance for many primary nitrate response genes, including the major high‐affinity nitrate transporters. Correspondingly, high‐affinity nitrate uptake and the transport of nitrate from roots to shoots are compromised inAtGRXS8‐overexpressing plants. Finally, we demonstrated that the AtGRXS8 protein can physically interact with the TGA1 and TGA4 transcription factors, which are central regulators of early transcriptional responses to nitrate inA. thalianaroots. Overall, these results suggest thatAtGRXS8acts to quench both transcriptional and developmental aspects of primary nitrate response, potentially by interfering with the activity of the TGA1 and TGA4 transcription factors. 

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2. Root-Knot-Nematode-Encoded CEPs Increase Nitrogen Assimilation

   https://doi.org/10.3390/life13102020  

   Mishra, Shova; Hu, Weiming; DiGennaro, Peter (October 2023, Life)

   C-terminally encoded peptides (CEPs) are plant developmental signals that regulate growth and adaptive responses to nitrogen stress conditions. These small signal peptides are common to all vascular plants, and intriguingly have been characterized in some plant parasitic nematodes. Here, we sought to discover the breadth of root-knot nematode (RKN)-encoded CEP-like peptides and define the potential roles of these signals in the plant–nematode interaction, focusing on peptide activity altering plant root phenotypes and nitrogen uptake and assimilation. A comprehensive bioinformatic screen identified 61 CEP-like sequences encoded within the genomes of six root-knot nematode (RKN; Meloidogyne spp.) species. Exogenous application of an RKN CEP-like peptide altered A. thaliana and M. truncatula root phenotypes including reduced lateral root number in M. truncatula and inhibited primary root length in A. thaliana. To define the role of RKN CEP-like peptides, we applied exogenous RKN CEP and demonstrated increases in plant nitrogen uptake through the upregulation of nitrate transporter gene expression in roots and increased 15N/14N in nematode-formed root galls. Further, we also identified enhanced nematode metabolic processes following CEP application. These results support a model of parasite-induced changes in host metabolism and inform endogenous pathways to regulate plant nitrogen assimilation. 

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3. The peptide GOLVEN10 alters root development and noduletaxis in Medicago truncatula

   https://doi.org/10.1111/tpj.16626  

   Roy, Sonali; Torres‐Jerez, Ivone; Zhang, Shulan; Liu, Wei; Schiessl, Katharina; Jain, Divya; Boschiero, Clarissa; Lee, Hee‐Kyung; Krom, Nicholas; Zhao, Patrick X; et al (May 2024, The Plant Journal)

   SUMMARY The conservation of GOLVEN (GLV)/ROOT MERISTEM GROWTH FACTOR (RGF) peptide encoding genes across plant genomes capable of forming roots or root‐like structures underscores their potential significance in the terrestrial adaptation of plants. This study investigates the function and role of GOLVEN peptide‐coding genes inMedicago truncatula. Five out of fifteen GLV/RGF genes were notably upregulated during nodule organogenesis and were differentially responsive to nitrogen deficiency and auxin treatment. Specifically, the expression ofMtGLV9andMtGLV10at nodule initiation sites was contingent upon the NODULE INCEPTION transcription factor. Overexpression of these five nodule‐induced GLV genes in hairy roots ofM. truncatulaand application of their synthetic peptide analogues led to a decrease in nodule count by 25–50%. Uniquely, the GOLVEN10 peptide altered the positioning of the first formed lateral root and nodule on the primary root axis, an observation we term ‘noduletaxis’; this decreased the length of the lateral organ formation zone on roots. Histological section of roots treated with synthetic GOLVEN10 peptide revealed an increased cell number within the root cortical cell layers without a corresponding increase in cell length, leading to an elongation of the root likely introducing a spatiotemporal delay in organ formation. At the transcription level, the GOLVEN10 peptide suppressed expression of microtubule‐related genes and exerted its effects by changing expression of a large subset of Auxin responsive genes. These findings advance our understanding of the molecular mechanisms by which GOLVEN peptides modulate root morphology, nodule ontogeny, and interactions with key transcriptional pathways. 

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4. Collagen Fibril Abnormalities in Human and Mice Abdominal Aortic Aneurysm

   Jones, B.; Tonniges, J. R.; Debsk, A.i; Albert, B.; Yeung, D. A.; Gadde, N.; Mahajan, A.; Sharma, N.; Calomeni, E. P.; Go, M.; et al (August 2020, Biomedical Engineering Society 2020 Annual Meeting)

   null (Ed.)

   Introduction: Vascular diseases like abdominal aortic aneurysms (AAA) are characterized by a drastic remodeling of the vessel wall, accompanied with changes in the elastin and collagen content. At the macromolecular level, the elastin fibers in AAA have been reported to undergo significant structural alterations. While the undulations (waviness) of the collagen fibers is also reduced in AAA, very little is understood about changes in the collagen fibril at the sub-fiber level in AAA as well as in other vascular pathologies. Materials and Methods: In this study we investigated structural changes in collagen fibrils in human AAA tissue extracted at the time of vascular surgery and in aorta extracted from angiotensin II (AngII) infused ApoE−/− mouse model of AAA. Collagen fibril structure was examined using transmission electron microscopy and atomic force microscopy. Images were analyzed to ascertain length and depth of D-periodicity, fibril diameter and fibril curvature. Tissues were also stained using collagen hybridizing peptide (CHP) and analyzed using fluorescent microscopy and second harmonic generation (SHG) microscopy to locate regions of healthy and degraded collagen. Results: Abnormal collagen fibrils with compromised D-periodic banding were observed in the excised human tissue and in remodeled regions of AAA in AngII infused mice (Figure 1). These abnormal fibrils were characterized by statistically significant reduction in depths of D-periods and an increased curvature of collagen fibrils. These features were more pronounced in human AAA as compared to murine samples. Additionally, regions of abnormal collagen were located within the remodeled areas of AAA tissue and were distinct from healthy collagen regions as ascertained using CHP staining and SHG (Figure 1). Thoracic aorta from Ang II-infused mice, abdominal aorta from saline-infused mice, and abdominal aorta from non-AAA human controls did not contain abnormal collagen fibrils. Conclusions: The structural alterations in abnormal collagen fibrils appear similar to those reported for collagen fibrils subjected to mechanical overload or chronic inflammation in other tissues. Detection of abnormal collagen could be utilized to better understand the functional properties of the underlying extracellular matrix in vascular as well as other pathologies. 

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5. ATAD3 Proteins: Unique Mitochondrial Proteins Essential for Life in Diverse Eukaryotic Lineages

   https://doi.org/10.1093/pcp/pcad122  

   Waters, Elizabeth R.; Bezanilla, Magdalena; Vierling, Elizabeth (October 2023, Plant And Cell Physiology)

   Abstract ATPase family AAA domain–containing 3 (ATAD3) proteins are unique mitochondrial proteins that arose deep in the eukaryotic lineage but that are surprisingly absent in Fungi and Amoebozoa. These ∼600-amino acid proteins are anchored in the inner mitochondrial membrane and are essential in metazoans and Arabidopsis thaliana. ATAD3s comprise a C-terminal ATPases Associated with a variety of cellular Activities (AAA+) matrix domain and an ATAD3_N domain, which is located primarily in the inner membrane space but potentially extends to the cytosol to interact with the ER. Sequence and structural alignments indicate that ATAD3 proteins are most similar to classic chaperone unfoldases in the AAA+ family, suggesting that they operate in mitochondrial protein quality control. A. thaliana has four ATAD3 genes in two distinct clades that appear first in the seed plants, and both clades are essential for viability. The four genes are generally coordinately expressed, and transcripts are highest in growing apices and imbibed seeds. Plants with disrupted ATAD3 have reduced growth, aberrant mitochondrial morphology, diffuse nucleoids and reduced oxidative phosphorylation complex I. These and other pleiotropic phenotypes are also observed in ATAD3 mutants in metazoans. Here, we discuss the distribution of ATAD3 proteins as they have evolved in the plant kingdom, their unique structure, what we know about their function in plants and the challenges in determining their essential roles in mitochondria. 

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