Sreenivasulu, N.; Radchuk, V.; Alawady, A.; Borisjuk, L.; Weier, D.; Staroske, N.; Fuchs, J.; Miersch, O.; Strickert, M.; Usadel, B.; Wobus, U.; Grimm, B.; Weber, H.; Weschke, W. De-regulation of abscisic acid contents causes abnormal endosperm development in the barley mutant seg8 Plant J 64(4), 589-603, (2010) DOI: 10.1111/j.1365-313X.2010.04350.x
Grain development of the maternal effect shrunken endosperm mutant seg8 was analysed by comprehensive molecular, biochemical and histological methods. The most obvious finding was de-regulation of ABA levels, which were lower compared to wild-type during the pre-storage phase but higher during the transition from cell division/differentiation to accumulation of storage products. Ploidy levels and ABA amounts were inversely correlated in the developing endosperms of both mutant and wild-type, suggesting an influence of ABA on cell-cycle regulation. The low ABA levels found in seg8 grains between anthesis and beginning endosperm cellularization may result from a gene dosage effect in the syncytial endosperm that causes impaired transfer of ABA synthesized in vegetative tissues into filial grain parts. Increased ABA levels during the transition phase are accompanied by higher chlorophyll and carotenoid/xanthophyll contents. The data suggest a disturbed ABA-releasing biosynthetic pathway. This is indicated by up-regulation of expression of the geranylgeranyl reductase (GGR) gene, which may be induced by ABA deficiency during the pre-storage phase. Abnormal cellularization/differentiation of the developing seg8 endosperm and reduced accumulation of starch are phenotypic characteristics that reflect these disturbances. The present study did not reveal the primary gene defect causing the seg8 phenotype, but presents new insights into the maternal/filial relationships regulating barley endosperm development.
Stumpe, M.; Göbel, C.; Faltin, B.; Beike, A. K.; Hause, B.; Himmelsbach, K.; Bode, J.; Kramell, R.; Wasternack, C.; Frank, W.; Reski, R.; Feussner, I. The moss Physcomitrella patens contains cyclopentenones but no jasmonates: mutations in allene oxide cyclase lead to reduced fertility and altered sporophyte morphology New Phytol 188 (3), 740-749, (2010) DOI: 10.1111/j.1469-8137.2010.03406.x
Two cDNAs encoding allene oxide cyclases (PpAOC1,
PpAOC2), key enzymes in the formation of jasmonic acid (JA) and its
precursor (9S,13S)‐12‐oxo‐phytodienoic acid (cis‐(+)‐OPDA), were
isolated from the moss Physcomitrella patens.Recombinant PpAOC1 and
PpAOC2 show substrate specificity against the allene oxide derived from
13‐hydroperoxy linolenic acid (13‐HPOTE); PpAOC2 also shows substrate
specificity against the allene oxide derived from 12‐hydroperoxy
arachidonic acid (12‐HPETE).In protonema and gametophores the occurrence
of cis‐(+)‐OPDA, but neither JA nor the isoleucine conjugate of JA nor
that of cis‐(+)‐OPDA was detected.Targeted knockout mutants for PpAOC1
and for PpAOC2 were generated, while double mutants could not be
obtained. The ΔPpAOC1 and ΔPpAOC2 mutants showed reduced fertility,
aberrant sporophyte morphology and interrupted sporogenesis.
Books and chapters
Yamaguchi, I.; Cohen, J. D.; Culler, A. H.; Quint, M.; Slovin, J. P.; Nakajima, M.; Yamaguchi, S.; Sakakibara, H.; Kuroha, T.; Hirai, N.; Yokota, T.; Ohta, H.; Kobayashi, Y.; Mori, H.; Sakagami, Y. Plant Hormones (Liu, H.-W. & Mander, L., eds.). Comprehensive Natural Products II 4, 9-125, (2010) ISBN: 978-0-08-045382-8 DOI: 10.1016/B978-008045382-8.00092-7
The definition of a plant hormone has not been clearly established, so
the compounds classified as plant hormones often vary depending on which
definition is considered. In this chapter, auxins, gibberellins (GAs),
cytokinins, abscisic acid, brassinosteroids, jasmonic acid-related
compounds, and ethylene are described as established plant hormones,
while polyamines and phenolic compounds are not included. On the other
hand, several peptides that have been proven to play a clear
physiological role(s) in plant growth and development, similar to the
established plant hormones, are referred. This chapter will focus
primarily on the more recent discoveries of plant hormones and their
impact on our current understanding of their biological role. In some
cases, however, it is critical to place recent work in a proper
The history of plant biology is inexorably
intertwined with the conception and discovery of auxin, followed by the
many decades of research to comprehend its action during growth and
development. Growth responses to auxin are complex and require the
coordination of auxin production, transport, and perception. In this
overview of past auxin research, we limit our discourse to the mechanism
of auxin action. We attempt to trace the almost epic voyage from the
birth of the hormonal concept in plants to the recent crystallographic
studies that resolved the TIR1-auxin receptor complex, the first
structural model of a plant hormone receptor. The century-long endeavor
is a beautiful illustration of the power of scientific reasoning and
human intuition, but it also brings to light the fact that decisive
progress is made when new technologies emerge and disciplines unite.
Delker, C.; Pöschl, Y.; Raschke, A.; Ullrich, K.; Ettingshausen, S.; Hauptmann, V.; Grosse, I.; Quint, M. Natural Variation of Transcriptional Auxin Response Networks in Arabidopsis thaliana Plant Cell 22, 2184-2200, (2010) DOI: 10.1105/tpc.110.073957
Natural variation has been observed for various traits in Arabidopsis thaliana. Here, we investigated natural variation in the context of physiological and transcriptional responses to the phytohormone auxin, a key regulator of plant development. A survey of the general extent of natural variation to auxin stimuli revealed significant physiological variation among 20 genetically diverse natural accessions. Moreover, we observed dramatic variation on the global transcriptome level after induction of auxin responses in seven accessions. Although we detect isolated cases of major-effect polymorphisms, sequencing of signaling genes revealed sequence conservation, making selective pressures that favor functionally different protein variants among accessions unlikely. However, coexpression analyses of a priori defined auxin signaling networks identified variations in the transcriptional equilibrium of signaling components. In agreement with this, cluster analyses of genome-wide expression profiles followed by analyses of a posteriori defined gene networks revealed accession-specific auxin responses. We hypothesize that quantitative distortions in the ratios of interacting signaling components contribute to the detected transcriptional variation, resulting in physiological variation of auxin responses among accessions.
Wasternack, C.; Kombrink, E. Jasmonates: Structural Requirements for Lipid-Derived Signals Active in Plant Stress Responses and Development ACS Chem Biol 5, 63-77, (2010) DOI: 10.1021/cb900269u
Jasmonates are lipid-derived signals that mediate plant stress responses and development processes. Enzymes participating in biosynthesis of jasmonic acid (JA) (1, 2) and components of JA signaling have been extensively characterized by biochemical and molecular-genetic tools. Mutants of Arabidopsis and tomato have helped to define the pathway for synthesis of jasmonoyl-isoleucine (JA-Ile), the active form of JA, and to identify the F-box protein COI1 as central regulatory unit. However, details of the molecular mechanism of JA signaling have only recently been unraveled by the discovery of JAZ proteins that function in transcriptional repression. The emerging picture of JA perception and signaling cascade implies the SCFCOI1 complex operating as E3 ubiquitin ligase that upon binding of JA-Ile targets JAZ repressors for degradation by the 26S-proteasome pathway, thereby allowing the transcription factor MYC2 to activate gene expression. The fact that only one particular stereoisomer, (+)-7-iso-JA-l-Ile (4), shows high biological activity suggests that epimerization between active and inactive diastereomers could be a mechanism for turning JA signaling on or off. The recent demonstration that COI1 directly binds (+)-7-iso-JA-l-Ile (4) and thus functions as JA receptor revealed that formation of the ternary complex COI1-JA-Ile-JAZ is an ordered process. The pronounced differences in biological activity of JA stereoisomers also imply strict stereospecific control of product formation along the JA biosynthetic pathway. The pathway of JA biosynthesis has been unraveled, and most of the participating enzymes are well-characterized. For key enzymes of JA biosynthesis the crystal structures have been established, allowing insight into the mechanisms of catalysis and modes of substrate binding that lead to formation of stereospecific products.
Wasternack, C.; Xie, D. The genuine ligand of a jasmonic acid receptor: Improved analysis of jasmonates is now required. Plant Signal Behav 5, 337-340, (2010) DOI: 10.4161/psb.5.4.11574
Jasmonic acid (JA), its metabolites, such as the methyl ester or amino acid conjugates as well as its precursor 12-oxophytodienoic acid (OPDA) are lipid-derived signals. JA, OPDA and JA-amino acid conjugates are known to function as signals in plant stress responses and development. More recently, formation of JA-amino acid conjugates and high biological activity of JA-Isoleucine (JA-Ile) were found to be essential in JA signaling. A breakthrough was the identification of JAZ proteins which interact with the F-box protein COI1 if JA-Ile is bound. This interaction leads to proteasomal degradation of JAZs being negative regulators of JA-induced transcription. Surprisingly, a distinct stereoisomer of JA-Ile, the (+)-7-iso-JA-Ile [(3R,7S) form] is most active. Coronatine, a bacterial phytotoxine with an identical stereochemistry at the cyclopentanone ring, has a similar bioactivity. This was explained by the recent identification of COI1 as the JA receptor and accords well with molecular modeling studies. Whereas over the last two decades JA was quantified to describe any JA dependent process, now we have to take into account a distinct stereoisomer of JA-Ile. Until recently a quantitative analysis of (+)-7-iso-JA-Ile was missing presumable due to its equilibration to (−)-JA-Ile. Now such an analysis was achieved. These aspects will be discussed based on our new knowledge on JA perception and signaling.
Ludwig-Müller, J.; Denk, K.; Cohen, J. D.; Quint, M. An Inhibitor of Tryptophan-Dependent Biosynthesis of Indole-3-Acetic Acid Alters Seedling Development in Arabidopsis J Plant Growth Regul 29, 242-248, (2010) DOI: 10.1007/s00344-009-9128-1
Although polar transport and the TIR1-dependent signaling pathway of the plant hormone auxin/indole-3-acetic acid (IAA) are well characterized, understanding of the biosynthetic pathway(s) leading to the production of IAA is still limited. Genetic dissection of IAA biosynthetic pathways has been complicated by the metabolic redundancy caused by the apparent existence of several parallel biosynthetic routes leading to IAA production. Valuable complementary tools for genetic as well as biochemical analysis of auxin biosynthesis would be molecular inhibitors capable of acting in vivo on specific or general components of the pathway(s), which unfortunately have been lacking. Several indole derivatives have been previously identified to inhibit tryptophan-dependent IAA biosynthesis in an in vitro system from maize endosperm. We examined the effect of one of them, 6-fluoroindole, on seedling development of Arabidopsis thaliana and tested its ability to inhibit IAA biosynthesis in feeding experiments in vivo. We demonstrated a correlation of severe developmental defects or growth retardation caused by 6-fluoroindole with significant downregulation of de novo synthesized IAA levels, derived from the stable isotope-labeled tryptophan pool, upon treatment. Hence, 6-fluoroindole shows important features of an inhibitor of tryptophan-dependent IAA biosynthesis both in vitro and in vivo and thus may find use as a promising molecular tool for the identification of novel components of the auxin biosynthetic pathway(s).
Robson, F.; Okamoto, H.; Patrick, E.; Harris, S.-R.; Wasternack, C.; Brearley, C.; Turner, J. G. Jasmonate and Phytochrome A Signaling in Arabidopsis Wound and Shade Responses Are Integrated through JAZ1 Stability Plant Cell 22, 1143-1160, (2010) DOI: 10.1105/tpc.109.067728
Jasmonate (JA) activates plant defense, promotes pollen maturation, and suppresses plant growth. An emerging theme in JA biology is its involvement in light responses; here, we examine the interdependence of the JA- and light-signaling pathways in Arabidopsis thaliana. We demonstrate that mutants deficient in JA biosynthesis and signaling are deficient in a subset of high irradiance responses in far-red (FR) light. These mutants display exaggerated shade responses to low, but not high, R/FR ratio light, suggesting a role for JA in phytochrome A (phyA) signaling. Additionally, we demonstrate that the FR lightinduced expression of transcription factor genes is dependent on CORONATINE INSENSITIVE1 (COI1), a central component of JA signaling, and is suppressed by JA. phyA mutants had reduced JA-regulated growth inhibition and VSP expression and increased content of cis-(+)-12-oxophytodienoic acid, an intermediate in JA biosynthesis. Significantly, COI1-mediated degradation of JASMONATE ZIM DOMAIN1-b-glucuronidase (JAZ1-GUS) in response to mechanical wounding and JA treatment required phyA, and ectopic expression of JAZ1-GUS resulted in exaggerated shade responses.Together, these results indicate that JA and phyA signaling are integrated through degradation of the JAZ1 protein, and both are required for plant responses to light and stress.
Renovell, Á.; Gago, S.; Ruiz-Ruiz, S.; Velázquez, K.; Navarro, L.; Moreno, P.; Vives, M. C.; Guerri, J. Mapping the subgenomic RNA promoter of the Citrus leaf blotch virus coat protein gene by Agrobacterium-mediated inoculation Virology 406, 360-369, (2010) DOI: 10.1016/j.virol.2010.07.034
Citrus leaf blotch virus has a single-stranded
positive-sense genomic RNA (gRNA) of 8747 nt organized in three open
reading frames (ORFs). The ORF1, encoding a polyprotein involved in
replication, is translated directly from the gRNA, whereas ORFs encoding
the movement (MP) and coat (CP) proteins are expressed via 3'
coterminal subgenomic RNAs (sgRNAs). We characterized the minimal
promoter region critical for the CP-sgRNA expression in infected cells
by deletion analyses using Agrobacterium-mediated infection of Nicotiana
benthamiana plants. The minimal CP-sgRNA promoter was mapped between
nucleotides −67 and + 50 nt around the transcription start site.
Surprisingly, larger deletions in the region between the CP-sgRNA
transcription start site and the CP translation initiation codon
resulted in increased CP-sgRNA accumulation, suggesting that this
sequence could modulate the CP-sgRNA transcription. Site-specific
mutational analysis of the transcription start site revealed that the
+ 1 guanylate and the + 2 adenylate are important for CP-sgRNA