COI1-dependent jasmonate signalling affects growth, metabolites production and cell wall protein composition in Arabidopsis

Background and Aims: Cultured cell suspensions have been the preferred model to study the apoplast as well as to monitor metabolic and cell cycle-related changes. Previous work showed that methyl jasmonate (MeJA) inhibits leaf growth in a CORONATINE INSENSITIVE 1 (COI1)-dependent manner, with COI1 being the jasmonate (JA) receptor. Here, the effect of COI1 overexpression on the growth of stably transformed arabidopsis cell cultures is described. Methods: Time-course experiments were carried out to analyse gene expression, and protein and metabolite levels. Key Results: Both MeJA treatment and the overexpression of COI1 modify growth, by altering cell proliferation and expansion. DNA content as well as transcript patterns of cell cycle and cell wall remodelling markers were altered. COI1 overexpression also increases the protein levels of OLIGOGALACTURONIDE OXIDASE 1, BETA-GLUCOSIDASE/ENDOGLUCANASES and POLYGALACTURONASE INHIBITING PROTEIN2, reinforcing the role of COI1 in mediating defence responses and highlighting a link between cell wall loosening and growth regulation. Moreover, changes in the levels of the primary metabolites alanine, serine and succinic acid of MeJA-treated Arabidopsis cell cultures were observed. In addition, COI1 overexpression positively affects the availability of metabolites such as β-alanine, threonic acid, putrescine, glucose and myo-inositol, thereby providing a connection between JA-inhibited growth and stress responses. Conclusions: This study contributes to the understanding of the regulation of growth and the production of metabolic resources by JAs and COI1. This will have important implications in dissecting the complex relationships between hormonal and cell wall signalling in plants. The work also provides tools to uncover novel mechanisms co-ordinating cell division and post-mitotic cell expansion in the absence of organ developmental control

Rapid transient induction of phenylalanine ammonia-lyase mRNA in elicitor-treated bean cells

DNAs complementary to a size-selected fraction of poly(A)(+) RNA present in elicitor-treated cells of bean (Phaseolus vulgaris L.) were inserted into pAT153 and used to transform Escherichia coli strain C600. Five clones were identified by hybrid-selected translation and cross-hybridization that contained sequences complementary to mRNA encoding phenylalanine ammonia-lyase (EC 4.3.1.5), which catalyzes the first reaction of phenylpropanoid biosynthesis. The longest insert contained a single open reading frame of 1520 base pairs together with 223 base pairs of 3′ untranslated sequence. RNA blot hybridization showed that elicitor caused a rapid, marked but transient increase in phenylalanine ammonia-lyase mRNA that was closely correlated with changes in translatable mRNA activity in vitro and enzyme synthesis in vivo. Blot hybridization of newly synthesized mRNA purified by organomercurial affinity chromatography following in vivo pulse-labeling with 4-thiouridine indicates that elicitor caused a rapid stimulation of phenylalanine ammonia-lyase mRNA synthesis as an early in the defense response leading to accumulation of phenylpropanoid-derived phytoalexins

Changes in patterns of protein synthesis during haustorial development of Striga hermonthica (del.) benth. seedlings

This study focuses upon the developmental transition of the parasitic plant Striga hermonthica from its freeliving state (germinated seedling) to its parasitic state after development of an infection organ: the haustorium. A new method has been developed that allows the production of gram quantities of germinated and haustorially-induced Striga seedlings, thereby facilitating biochemical and molecular analysis of haustorial induction. Water-soluble proteins have been extracted from germinated seeds (stage A) and seedlings treated with 2,6-dimethoxy-p-benzoquinone (2,6-DMBQ) to induce haustorium (stage B). Samples were analysed by two-dimensional polyacrylamide gel electrophoresis and quantitative as well as qualitative differences could be observed. In particular a group of four highly abundant acidic proteins (molecular weight 39 kDa, pl 5.1, 5.3, 5.3, 5.6) and three other proteins (molecular weight 12 kDa, pl 6.9; 17 kDa, pl 4.4; 17 kDa, pl 4.45) were seen in stage A while at least four proteins (molecular weight 21.5 kDa, pl 6.4; 21.5 kDa, pl 6.3; 31 kDa, pl 5.1; 34 kDa, pl 6.2) were present in greater abundance in stage B. In order to compare watersoluble protein with newly synthesized protein patterns, mRNAs from the two stages of development were isolated and cell-free translation products analysed by 2-D PAGE. Two-D gels of cell-free translation products showed the appearance of six proteins in stage B (molecular weight ranging from 10 to 35 kDa) and the presence of three acidic proteins in stage A with one protein (molecular weight 40 kDa) very similar in size to the triplet of proteins in the water-soluble protein 2-D gels