ABSTRACT
Brassica napus L. is an important crop plant, characterised by high nitrogen (N) levels in fallen leaves, leading to a significant restitution of this element to the soil, with important consequences at the economic and environmental levels. It is now well established that the N in fallen leaves is due to weak N remobilisation that is especially related to incomplete degradation of foliar proteins during leaf senescence. Identification of residual proteins in a fallen leaf (i.e. incompletely degraded in the last step of the N remobilisation process) constitutes important information for improving nutrient use efficiency. Proteome analysis of the vascular system (petioles) and blades from fallen leaves of Brassica napus was performed, and the 30 most abundant residual proteins in each tissue were identified. Among them, several proteins involved in N recycling remain in the leaf after abscission. Moreover, this study reveals that some residual proteins are associated with energy metabolism, protection against oxidative stress, and more surprisingly, photosynthesis. Finally, comparison of blade and petiole proteomes show that, despite their different physiological roles in the non-senescing leaf, both organs redirect their metabolism in order to ensure catabolic reactions. Taken together, the results suggest that a better degradation of these leaf proteins during the senescence process could enable improvements in the N use efficiency of Brassica napus.
Subject(s)
Brassica napus/metabolism , Plant Leaves/metabolism , Plant Proteins/metabolism , Proteomics/methods , Biodegradation, Environmental , Nitrogen , Plant Proteins/analysisABSTRACT
The gene, indole-3-butyric acid (IBA)-RESPONSE (IBR) 3, is thought to participate in peroxisomal ß-oxidation of IBA to indole-3-acetic acid. Here we show that IBR3 may also play a role in Arabidopsis thaliana defence response to microbial pathogens. IBR3 is up-regulated during infection by virulent Pseudomonas syringae pv. tomato (Pst) DC3000 bacteria. Although mutant ibr3-4 did not show a pathogen phenotype, lines overexpressing IBR3 demonstrated enhanced susceptibility to Pst DC3000. Increased susceptibility phenotypes of IBR3 overexpressors were correlated with defective SA defence signalling and impairment of pattern-triggered immunity (PTI) activation. Notably, reactive oxygen species production was reduced in IBR3 overexpressors after treatment with the microbe-associated molecular patterns flg22 and efl26. Later PTI responses, such as accumulation of FRK1 transcripts and callose deposition were also reduced in transgenics overexpressing IBR3 after inoculation with the Type III secretion system deficient bacterial mutant Pst DC3000 hrcC or treatment with flg22 or elf26. Importantly, overexpression of IBR3 did not affect indole-3-acetic acid content or auxin-responsive gene expression. These results suggest a novel role for IBR3 in A. thaliana defence response against bacterial pathogens.
