chlorophyll-a and proanthocyanidin

Plant pathogenic bacteria disseminate and survive mainly in association with seeds. This study addresses whether seeds are passive carriers or engage a molecular dialogue with pathogens during their development. We developed two pathosystems using Medicago truncatula with Xanthomonas alfalfae subsp. alfalfae (Xaa), the natural Medicago sp. pathogen and Xanthomonas campestris pv. campestris (Xcc), a Brassicaceae pathogen. Three days after flower inoculation, the transcriptome of Xcc-infected pods showed activation of an innate immune response that was strongly limited in Xcc mutated in the type three secretion system, demonstrating an incompatible interaction of Xcc with the reproductive structures. In contrast, the presence of Xaa did not result in an activation of defence genes. Transcriptome profiling during development of infected seeds exhibited time-dependent and differential responses to Xcc and Xaa. Gene network analysis revealed that the transcriptome of Xcc-infected seeds was mainly affected during seed filling whereas that of Xaa-infected seeds responded during late maturation. The Xcc-infected seed transcriptome exhibited an activation of defence response and a repression of targeted seed maturation pathways. Fifty-one percent of putative ABSCISIC ACID INSENSITIVE3 targets were deregulated by Xcc, including oleosin, cupin, legumin and chlorophyll degradation genes. At maturity, these seeds displayed decreased weight and increased chlorophyll content. In contrast, these traits were not affected by Xaa infection. These findings demonstrate the existence of a complex molecular dialogue between xanthomonads and developing seeds and provides insights into a previously unexplored trade-off between seed development and pathogen defence.

Topics: Chlorophyll; Epigenesis, Genetic; Flowers; Gene Expression Profiling; Gene Expression Regulation, Plant; Gene Ontology; Gene Regulatory Networks; Genes, Plant; Host-Pathogen Interactions; Medicago truncatula; Organ Size; Plant Diseases; Plant Proteins; Proanthocyanidins; Reproduction; RNA, Messenger; Seeds; Stress, Physiological; Time Factors; Transcriptome; Xanthomonas

Apart from red (chlorophyll a) fluorescence, ultraviolet (UV) excitation of plant leaves results in blue-green intrinsic light emission. In order to analyse the potentially modifying influence of stress on this blue-green fluorescence (BGF), and to determine its origin, the fluorescence was characterised by spectroscopy, and two and three dimensional microscopy in leaves of Hordeum vulgare L. under UV and drought stress. Leaves of wild-type and proanthocyanidin-free mutant barley were compared. In general, the BGF was enhanced by stress. The analysis of the distribution of BGF pointed to differences in response to the different stress conditions and served to indicate possible sources of the fluorescence. This study showed that (1) the selective enhancement of BGF by supplementary UV radiation (280-360 nm) in upper leaf tissues of wild-type but not in proanthocyanidin-free leaves, pointed to flavonoids as possible emitters; (2) drought-inducible BGF emission was found in cell walls and to a smaller extent in upper leaf tissue regardless of genotype, thus independent of impairment in flavonoid biosynthesis and (3) intracellular BGF, which co-localised with red chlorophyll fluorescence, was inducible in mesophyll cells of both genotypes by short-term application of high levels of UV radiation.

Topics: Anthocyanins; Chlorophyll; Dehydration; Fluorescence; Hordeum; Microscopy, Confocal; Plant Leaves; Proanthocyanidins; Spectrometry, Fluorescence; Time Factors; Ultraviolet Rays