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Chutia, R.; Abel, S.; Ziegler, J. Iron and Phosphate Deficiency Regulators Concertedly Control Coumarin Profiles in Arabidopsis thaliana Roots During Iron, Phosphate, and Combined Deficiencies Front Plant Sci 10, 113, (2019) DOI: 10.3389/fpls.2019.00113

Plants face varying nutrient conditions, to which they have to adapt to. Adaptive responses are nutrient-specific and strategies to ensure supply and homeostasis for one nutrient might be opposite to another one, as shown for phosphate (Pi) and iron (Fe) deficiency responses, where many genes are regulated in an opposing manner. This was also observed on the metabolite levels. Whereas root and exudate levels of catechol-type coumarins, phenylpropanoid-derived 2-benzopyranones, which facilitate Fe acquisition, are elevated after Fe deficiency, they are decreased after Pi deficiency. Exposing plants to combined Pi and Fe deficiency showed that the generation of coumarin profiles in Arabidopsis thaliana roots by Pi deficiency considerably depends on the availability of Fe. Similarly, the effect of Fe deficiency on coumarin profiles is different at low compared to high Pi availability. These findings suggest a fine-tuning of coumarin profiles, which depends on Fe and Pi availability. T-DNA insertion lines exhibiting aberrant expression of genes involved in the regulation of Pi starvation responses (PHO1, PHR1, bHLH32, PHL1, SPX1) and Fe starvation responses (BRUTUS, PYE, bHLH104, FIT) were used to analyze the regulation of the generation of coumarin profiles in Arabidopsis thaliana roots by Pi, Fe, and combined Pi and Fe deficiency. The analysis revealed a role of several Fe-deficiency response regulators in the regulation of Fe and of Pi deficiency-induced coumarin profiles as well as for Pi deficiency response regulators in the regulation of Pi and of Fe deficiency-induced coumarin profiles. Additionally, the regulation of Fe deficiency-induced coumarin profiles by Fe deficiency response regulators is influenced by Pi availability. Conversely, regulation of Pi deficiency-induced coumarin profiles by Pi deficiency response regulators is modified by Fe availability.

Wasternack, C.; Hause, B. Jasmonates: biosynthesis, perception, signal transduction and action in plant stress response, growth and development. An update to the 2007 review in <span>Annals of Botany</span> Annals of Botany 111, 1021-1058, (2013) DOI: 10.1093/aob/mct067

Background: Jasmonates are important regulators in plant responses to biotic and abiotic stresses as well as indevelopment. Synthesized from lipid-constituents, the initially formed jasmonic acid is converted to differentmetabolites including the conjugate with isoleucine. Important new components of jasmonate signalling includingits receptor were identified, providing deeper insight into the role of jasmonate signalling pathways in stressresponses and development.Scope: The present review is an update of the review on jasmonates published in this journal in 2007. New dataof the last five years are described with emphasis on metabolites of jasmonates, on jasmonate perception andsignalling, on cross-talk to other plant hormones and on jasmonate signalling in response to herbivores and pathogens,in symbiotic interactions, in flower development, in root growth and in light perception.Conclusions: The last few years have seen breakthroughs in the identification of JASMONATE ZIM DOMAIN(JAZ) proteins and their interactors such as transcription factors and co-repressors, and the crystallization of thejasmonate receptor as well as of the enzyme conjugating jasmonate to amino acids. Now, the complex nature ofnetworks of jasmonate signalling in stress responses and development including hormone cross-talk can beaddressed.

Janitza, P.; Ullrich, K. K.; Quint, M. Toward a comprehensive phylogenetic reconstruction of the evolutionary history of mitogen-activated protein kinases in the plant kingdom Front Plant Sci 3, 271, (2012) DOI: 10.3389/fpls.2012.00271

The mitogen-activated protein kinase (MAPK) pathway is a three-tier signaling cascade that transmits cellular information from the plasma membrane to the cytoplasm where it triggers downstream responses. The MAPKs represent the last step in this cascade and are activated when both tyrosine and threonine residues in a conserved TxY motif are phosphorylated by MAPK kinases, which in turn are themselves activated by phosphorylation by MAPK kinase kinases. To understand the molecular evolution of MAPKs in the plant kingdom, we systematically conducted a Hidden-Markov-Model based screen to identify MAPKs in 13 completely sequenced plant genomes. In this analysis, we included green algae, bryophytes, lycophytes, and several mono- and eudicotyledonous species covering >800 million years of evolution. The phylogenetic relationships of the 204 identified MAPKs based on Bayesian inference facilitated the retraction of the sequence of emergence of the four major clades that are characterized by the presence of a TDY or TEY-A/TEY-B/TEY-C type kinase activation loop. We present evidence that after the split of TDY- and TEY-type MAPKs, initially the TEY-C clade emerged. This was followed by the TEY-B clade in early land plants until the TEY-A clade finally emerged in flowering plants. In addition to these well characterized clades, we identified another highly conserved clade of 45 MAPK-likes, members of which were previously described as Mak-homologous kinases. In agreement with their essential functions, molecular population genetic analysis of MAPK genes in Arabidopsis thaliana accessions reveal that purifying selection drove the evolution of the MAPK family, implying strong functional constraints on MAPK genes. Closely related MAPKs most likely subfunctionalized, a process in which differential transcriptional regulation of duplicates may be involved.

Abel, S.; Köck, M. Secretory ribonucleases from tomato (Lycopersicon esculentum cv. Mill.) Meth Enzymol 341, 351 - 368, (2001)

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