Differential expression and cellular localization of ERKs during organogenic nodule formation from internodes of Humulus lupulus var. Nugget

Arginine Decarboxylase expression, polyamines biosynthesis and reactive oxygen species during organogenic nodule formation in hop

Hop (Humulus lupulus L.) is an economically important plant species used in beer production and as a health-promoting medicine. Hop internodes develop upon stress treatments organogenic nodules which can be used for genetic transformation and micropropagation. Polyamines are involved in plant development and stress responses. Arginine decarboxylase (ADC; EC 4·1.1·19) is a key enzyme involved in the biosynthesis of putrescine in plants. Here we show that ADC protein was increasingly expressed at early stages of hop internode culture (12h). Protein continued accumulating until organogenic nodule formation after 28 days, decreasing thereafter. The same profile was observed for ADC transcript suggesting transcriptional regulation of ADC gene expression during morphogenesis. The highest transcript and protein levels observed after 28 days of culture were accompanied by a peak in putrescine levels. Reactive oxygen species accumulate in nodular tissues probably due to stress inherent to in vitro conditions and enhanced polyamine catabolism. Conjugated polyamines increased during plantlet regeneration from nodules suggesting their involvement in plantlet formation and/or in the control of free polyamine levels. Immunogold labeling revealed that ADC is located in plastids, nucleus and cytoplasm of nodular cells. In vacuolated cells, ADC immunolabelling in plastids doubled the signal of proplastids in meristematic cells. Location of ADC in different subcellular compartments may indicate its role in metabolic pathways taking place in these compartments. Altogether these data suggest that polyamines play an important role in organogenic nodule formation and represent a progress towards understanding the role played by these growth regulators in plant morphogenesis.

Organogenic nodule formation in hop: a tool to study morphogenesis in plants with biotechnological and medicinal applications

The usage of Humulus lupulus for brewing increased the demand for high-quality plant material. Simultaneously, hop has been used in traditional medicine and recently recognized with anticancer and anti-infective properties. Tissue culture techniques have been reported for a wide range of species, and open the prospect for propagation of disease-free, genetically uniform and massive amounts of plants in vitro. Moreover, the development of large-scale culture methods using bioreactors enables the industrial production of secondary metabolites. Reliable and efficient tissue culture protocol for shoot regeneration through organogenic nodule formation was established for hop. The present review describes the histological, and biochemical changes occurring during this morphogenic process, together with an analysis of transcriptional and metabolic profiles. We also discuss the existence of common molecular factors among three different morphogenic processes: organogenic nodules and somatic embryogenesis, which strictly speaking depend exclusively on intrinsic developmental reprogramming, and legume nitrogen-fixing root nodules, which arises in response to symbiosis. The review of the key factors that participate in hop nodule organogenesis and the comparison with other morphogenic processes may have merit as a study presenting recent advances in complex molecular networks occurring during morphogenesis and together, these provide a rich framework for biotechnology applications.

Organogenic nodule development in hop (Humulus lupulus L.): transcript and metabolic responses

BACKGROUND

Hop (Humulus lupulus L.) is an economically important plant forming organogenic nodules which can be used for genetic transformation and micropropagation. We are interested in the mechanisms underlying reprogramming of cells through stress and hormone treatments.

RESULTS

An integrated molecular and metabolomic approach was used to investigate global gene expression and metabolic responses during development of hop's organogenic nodules. Transcript profiling using a 3,324-cDNA clone array revealed differential regulation of 133 unigenes, classified into 11 functional categories. Several pathways seem to be determinant in organogenic nodule formation, namely defense and stress response, sugar and lipid metabolism, synthesis of secondary metabolites and hormone signaling. Metabolic profiling using 1H NMR spectroscopy associated to two-dimensional techniques showed the importance of metabolites related to oxidative stress response, lipid and sugar metabolism and secondary metabolism in organogenic nodule formation.

CONCLUSION

The expression profile of genes pivotal for energy metabolism, together with metabolites profile, suggested that these morphogenic structures gain energy through a heterotrophic, transport-dependent and sugar-degrading anaerobic metabolism. Polyamines and auxins are likely to be involved in the regulation of expression of many genes related to organogenic nodule formation. These results represent substantial progress toward a better understanding of this complex developmental program and reveal novel information regarding morphogenesis in plants.

Identification and subcellular localization of the soybean copper P1B-ATPase GmHMA8 transporter

We have identified a copper P(1B)-ATPase transporter in soybean (Glycine max), named as GmHMA8, homologue to cyanobacterial PacS and Arabidopsis thaliana AtHMA8 (PAA2) transporters. A novel specific polyclonal anti-GmHMA8 antibody raised against a synthetic peptide reacted with a protein of an apparent mass of around 180-200 kDa in chloroplast and thylakoid membrane preparations isolated from soybean cell suspensions. Immunoblot analysis with this antibody also showed a band with similar apparent molecular mass in chloroplasts from Lotus corniculatus. Immunofluorescence labelling with the anti-GmHMA8 antibody and double immunofluorescence labelling with anti-GmHMA8 and anti-RuBisCo antibodies revealed the localization of the GmHMA8 transporter within the chloroplast organelle. Furthermore, the precise ultrastructural distribution of GmHMA8 within the chloroplast subcompartments was demonstrated by using electron microscopy immunogold labelling. The GmHMA8 copper transporter from soybean was localized in the thylakoid membranes showing a heterogeneous distribution in small clusters.

Expression of allene oxide cyclase and accumulation of jasmonates during organogenic nodule formation from hop (Humulus lupulus var. Nugget) internodes

A crucial step in the biosynthesis of jasmonic acid (JA) is the formation of its stereoisomeric precursor, cis-(+)-12-oxophytodienoic acid (OPDA), which is catalyzed by allene oxide cyclase (AOC, EC 5.3.99.6). A cDNA of AOC was isolated from Humulus lupulus var. Nugget. The ORF of 765 bp encodes a 255 amino acid protein, which carries a putative chloroplast targeting sequence. The recombinant protein without its putative chloroplast target sequence showed significant AOC activity. Previously we demonstrated that wounding induces organogenic nodule formation in hop. Here we show that the AOC transcript level increases in response to wounding of internodes, peaking between 2 and 4 h after wounding. In addition, Western blot analysis showed elevated levels of AOC peaking 24 h after internode inoculation. The AOC increase was accompanied by increased JA levels 24 h after wounding, whereas OPDA had already reached its highest level after 12 h. AOC is mostly present in the vascular bundles of inoculated internodes. During prenodule and nodule formation, AOC levels were still high. JA and OPDA levels decreased down to 10 and 118 pmol (g FW)(-1), respectively, during nodule formation, but increased during plantlet regeneration. Double immunolocalization analysis of AOC and Rubisco in connection with lugol staining showed that AOC is present in amyloplasts of prenodular cells and in the chloroplasts of vacuolated nodular cells, whereas meristematic cells accumulated little AOC. These data suggest a role of AOC and jasmonates in organogenic nodule formation and plantlet regeneration from these nodules.

Mitogen-activated protein kinases are developmentally regulated during stress-induced microspore embryogenesis in Brassica napus L

Plant mitogen-activated protein kinase (MAPK) cascades are involved in extracellular stress signalling pathways, leading to different cellular responses. Stress-induced microspore embryogenesis involves the internalization of an extracellular stress signal, generating a number of cellular responses where MAPK cascades might be involved. These responses include a change of the developmental programme, the entry into an early proliferative stage and, subsequently, into differentiation stages during haploid embryogenesis. In this work we studied the expression during microspore embryogenesis of several kinases, to assess their putative role in these events. The known Brassica napus MAP kinase kinase kinases (MAP3Ks BnMAP3Kalpha1, BnMAP3Kbeta1 and BnMAP3Kepsilon, the BnBSKtheta kinase and B. napus extracellular signal-regulated kinase (ERK) homologues were analysed by electron microscope (EM) in situ hybridization, immuno-gold labelling, immunofluorescence and western blotting. The differential in situ expression of these kinases suggests a role for them during embryogenesis. Two different expression patterns were observed, indicating a different regulation. BnMAP3Kalpha1, BnMAP3Kepsilon, and the ERKs showed a pattern consistent with a role mainly in proliferative events. Conversely, BnMAP3Kbeta1 and BnBSKtheta, presented a pattern that suggested an involvement in differentiation stages. In addition, ERK homologues migrate to the nucleus immediately after induction, being found in a phosphorylated state in a larger amount.