The effect on the transcriptome of Anemone coronaria following infection with rust (Tranzschelia discolor).

In order to understand plant/pathogen interaction, the transcriptome of uninfected (1S) and infected (2I) plant was sequenced at 3'end by the GS FLX 454 platform. De novo assembly of high-quality reads generated 27,231 contigs leaving 37,191 singletons in the 1S and 38,393 in the 2I libraries. ESTcalc tool suggested that 71% of the transcriptome had been captured, with 99% of the genes present being represented by at least one read. Unigene annotation showed that 50.5% of the predicted translation products shared significant homology with protein sequences in GenBank. In all 253 differential transcript abundance (DTAs) were in higher abundance and 52 in lower abundance in the 2I library. 128 higher abundance DTA genes were of fungal origin and 49 were clearly plant sequences. A tBLASTn-based search of the sequences using as query the full length predicted polypeptide product of 50 R genes identified 16 R gene products. Only one R gene (PGIP) was up-regulated. The response of the plant to fungal invasion included the up-regulation of several pathogenesis related protein (PR) genes involved in JA signaling and other genes associated with defense response and down regulation of cell wall associated genes, non-race-specific disease resistance1 (NDR1) and other genes like myb, presqualene diphosphate phosphatase (PSDPase), a UDP-glycosyltransferase 74E2-like (UGT). The DTA genes identified here should provide a basis for understanding the A. coronaria/T. discolor interaction and leads for biotechnology-based disease resistance breeding.

Ectopic expression of Kxhkn5 in the viviparous species Kalanchoe × Houghtonii induces a novel pattern of epiphyll development.

KxhKN5 (class 1 KNOX gene) was cloned from Kalanchoe × houghtonii with strong tendency to form epiphylls on leaves. KxhKN5 appear to be homologue of BP of A. thaliana on the basis of phylogeny, expression and phenotype analysis. Beside the modification of several plant and leaf traits, the appearance of epiphylls was drastically reduced by both the silencing and the over-expression of KxhKN5 in most of the generated clones. In silenced clones, epiphyll production followed the morphogenetic pathway of the WT plants: somatic embryos outbreak in the centre of each leaf-pedestal, grown in the notch between leaf indentations and were supported by a suspensor. The connection between the epiphyll and the mother plant did not include any vasculature and as a result, the epiphylls dropped easily from the mother plant. The most represented category of over expressor clones, disclosed a novel pattern of epiphyll development: the leaf-pedestals were absent and single bud outbreaks in each leaf notch. Buds developed into shoots which remained attached to the maternal plant by a strong vascular connection. The leaves supporting shoots, produced a thickened midrib and veins, and their lamina ceased expanding. Finally, the leaf/shoot structure resembles a lateral branch. The ectopic expression of KxhKN5 in K. × houghtonii induces a process comparable to the alternation of leaf and shoot formation in other species and support the idea, that it is the variation in shared molecular and developmental processes which produces the growth of specific structures.

Expression of KxhKN4 and KxhKN5 genes in Kalanchoë blossfeldiana 'Molly' results in novel compact plant phenotypes: towards a cisgenesis alternative to growth retardants.

Many potted plants like Kalanchoë have an elongated natural growth habit, which has to be controlled through the application of growth regulators. These chemicals will be banned in the near future in all the EU countries. Besides their structural functions, the importance of homeotic genes to modify plant architecture appears evident. In this work, the full length cDNA of five KNOX (KN) genes were sequenced from K. x houghtonii, a viviparous hybrid. Two constructs with the coding sequence of the class I and class II homeobox KN genes, KxhKN5 and KxhKN4, respectively, were overexpressed in the commercially important ornamental Kalanchoë blossfeldiana 'Molly'. Furthermore, a post-transcriptional gene silencing construct was made with a partial sequence of KxhKN5 and also transformed into 'Molly'. Several transgenic plants exhibited compact phenotypes and some lines had a relative higher number of inflorescences. A positive correlation between gene expression levels and the degree of compactness was found. However, a correlation between the induced phenotypes and the number of inserted copies of the transgene were not observed, although line '70-10' with a high copy number also had the highest expression level. Moreover, overexpression of KxhKN4 resulted in plants with dark green leaves due to an elevated content of chlorophyll, a highly desired property in the ornamental plant industry. These transgenic plants show that a cisgenesis approach towards production of compact plants with improved quality as an alternative to chemical growth retardants may be feasible.

Metabolic response to cold and freezing of Osteospermum ecklonis overexpressing Osmyb4.

The constitutive expression of the rice Osmyb4 gene in Arabidopsis plants gives rise to enhanced abiotic and biotic stress tolerance, probably by activating several stress-inducible pathways. However, the effect of Osmyb4 on stress tolerance likely depends on the genetic background of the transformed species. In this study, we explored the potential of Osmyb4 to enhance the cold and freezing tolerance of Osteospermum ecklonis, an ornamental and perennial plant native to South Africa, because of an increasing interest in growing this species in Europe where winter temperatures are low. Transgenic O. ecklonis plants were obtained through transformation with the Osmyb4 rice gene under the control of the CaMV35S promoter. We examined the phenotypic adaptation of transgenic plants to cold and freezing stress. We also analysed the ability of wild-type and transgenic Osteospermum to accumulate several solutes, such as proline, amino acids and sugars. Using nuclear magnetic resonance, we outlined the metabolic profile of this species under normal growth conditions and under stress for the first time. Indeed, we found that overexpression of Osmyb4 improved the cold and freezing tolerance and produced changes in metabolite accumulation, especially of sugars and proline. Based on our data, it could be of agronomic and economic interest to use this gene to produce Osteospermum plants capable of growing in open field, even during the winter season in climatic zone Z9.