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Publications - Cell and Metabolic Biology
Publications
The importance of phytohormone balance is increasingly recognized as central to the outcome of plant–pathogen interactions. Next to their well-known developmental role, brassinosteroids (BR) were recently found to be involved in plant innate immunity. In this study, we examined the role of BR in rice (Oryza sativa) innate immunity during infection with the root-knot nematode Meloidogyne graminicola, and we studied the inter-relationship with the jasmonate (JA) pathway. Exogenous epibrassinolide (BL) supply at low concentrations induced susceptibility in the roots whereas high concentrations of BL enforced systemic defense against this nematode. Upon high exogenous BL supply on the shoot, quantitative reverse-transcription polymerase chain reaction (qRT-PCR) confirmed a strong feedback inhibitory effect, leading to reduced BR biosynthesis in the root. Moreover, we demonstrate that the immune suppressive effect of BR is at least partly due to negative cross-talk with the JA pathway. Mutants in the BR biosynthesis or signaling pathway accumulate slightly higher levels of the immediate JA-precursor 12-oxo-phytodienoic acid, and qRT-PCR data showed that the BR and JA pathway are mutually antagonistic in rice roots. Collectively, these results suggest that the balance between the BR and JA pathway is an effective regulator of the outcome of the rice–M. graminicola interaction.
Publications
The nodule-specific MtNOD25 gene of the model legume Medicago truncatula encodes a modular nodulin composed of different repetitive modules flanked by distinct N- and C-termini. Although similarities are low with respect to all repetitive modules, both the N-terminal signal peptide (SP) and the C-terminus are highly conserved in modular nodulins from different legumes. On the cellular level, MtNOD25 is only transcribed in the infected cells of root nodules, and this activation is mediated by a 299-bp minimal promoter containing an organ-specific element. By expressing mGFP6 translational fusions in transgenic nodules, we show that MtNOD25 proteins are exclusively translocated to the symbiosomes of infected cells. This specific targeting only requires an N-terminal MtNOD25 SP that is highly conserved across a family of legume-specific symbiosome proteins. Our finding sheds light on one possible mechanism for the delivery of host proteins to the symbiosomes of infected root nodule cells and, in addition, defines a short molecular address label of only 24 amino acids whose N-terminal presence is sufficient to translocate proteins across the peribacteroid membrane.
Publications
A T-DNA insertion mutant of FUSCA3 (fus3-T) in Arabidopsis thaliana exhibits several of the expected deleterious effects on seed development, but not the formation of brown seeds, a colouration which results from the accumulation of large amounts of anthocyanin. A detailed phenotypic comparison between fus3-T and a known splice point mutant (fus3-3) revealed that the seeds from both mutants do not enter dormancy and can be rescued at an immature stage. Without rescue, mature fus3-3 seeds are non-viable, whereas those of fus3-T suffer only a slight loss in their germinability. A series of comparisons between the two mutants uncovered differences with respect to conditional lethality, in histological and sub-cellular features, and in the relative amounts of various storage compounds and metabolites present, leading to a further dissection of developmental processes in seeds and a partial reinterpretation of the complex seed phenotype. FUS3 function is now known to be restricted to the acquisition of embryo-dependent seed dormancy, the determination of cotyledonary cell identity, and the synthesis and accumulation of storage compounds. Based on DNA binding studies, a model is presented which can explain the differences between the mutant alleles. The fus3-T lesion is responsible for loss of function only, while the fus3-3 mutation induces various pleiotropic effects conditioned by a truncation gene product causing severe mis-differentiation.
This page was last modified on 27 Jan 2025 .
