75 Integrating Membrane Transport with Male Gametophyte ... - TAIR

291 The NIMIN-NPR1 Connection: A Molecular Switch that Controls the Expression of PR Genes
Ursula Pfitzner, Sylvia Zwicker, Vlatka Stos
Universitaet Hohenheim
NPR1 (also known as NIM1) is a positive key regulator of systemic acquired resistance (SAR) in Arabidopsis.
Upon salicylic acid (SA) induction, oligomeric NPR1 localized in the cytoplasm is mobilized (Mou et al., 2003). NPR1
monomers enter the nucleus, and transcription of pathogenesis-related (PR) genes starts (Kinkema et al., 2000). NPR1
interacts with two classes of proteins, TGA transcription factors (Zhang et al., 1999) and a group of novel proteins,
termed NIMIN proteins (NIMIN = NIM1 interacting protein; Weigel et al., 2001, 2005). In Arabidopsis, NIMIN1,
NIMIN2, and NIMIN3 constitute a small gene family of structurally related, yet distinct members. NIMIN-type genes
are found throughout the plant kingdom. G8-1, for example, a tobacco NIMIN homolog, has been reported to be rapidly
and sensitively induced by SA (Horvath et al., 1998). Likewise, both the Arabidopsis NIMIN1 and NIMIN2 promoters
are responsive to SA (Glocova et al., 2005).
To unravel their biological function, we have started to characterize the tobacco NIMIN group. cDNA clones were
isolated encoding G8-1 (from here on called NtNIMIN2a) and two novel family members. The NtNIMIN proteins
are structurally related to each other exhibiting the highest similarity to AtNIMIN2. For functional studies, we have
expressed a 35S::NtNIMIN2a chimeric gene and a NtNIMIN2a RNAi construct in tobacco. While overexpression of
NtNIMIN2a inhibited PR-1 proteins, suppression of NtNIMIN2 transcripts led to enhanced PR-1 protein accumulation.
In both cases, the effects of altered NtNIMIN2 transcript levels became evident foremost at the onset of SAR, indicating
that NtNIMIN2 proteins repress PR-1 genes transiently. We suggest that NIMIN proteins are positive regulators of the
SAR response that supervise PR gene expression through a novel mechanism termed signal-mediated pre-transcriptional
control (SIMPC). SIMPC may provide the molecular basis for the phenomenon of priming. In Arabidopsis, SIMPC has
adopted to the different lifestyle of the plant. Consequently, control of PR gene expression is mediated by distinct types
of NIMIN proteins, NIMIN1, NIMIN2, and NIMIN3.
292 Arabidopsis thaliana; A Naive Species To Study Plant/Virus Interactions
Veronique Decroocq, Micheline Lansac, Hien Le, Ophelie Sicard, Thierry Candresse, Olivier Le Gall, Frederic Revers
UMR GDPP, INRA Bordeaux-Universite Bordeaux2, BP81, 33883 Villenave d'Ornon Cedex, France. http://
www.bordeaux.inra.fr/ipv/
The virus cycle of infection in plant is a complex process that includes the expression of the viral genome, suppression of
host defences, virus replication, cell-to-cell movement via plasmodesmata and long distance movement through the vascular
system. This multi-step process requires interactions between factors from both the host and the virus. Unfortunately until
now, very few host factors have been identified.
In the aim to identify such factors, Arabidopsis thaliana accessions were challenged with isolates of two potyviruses,
Plum pox virus (PPV) and Lettuce mosaic virus (LMV), which naturally infect Prunus and Lactuca species respectively.
A high level of variability was observed both in the behaviour of LMV (1) and PPV (2) isolates and in that of the various
accessions tested, suggesting a high level of diversity of interactions within these naive Arabidopsis/potyvirus pathosystems.
Phenotypes ranged from complete systemic invasion, accompanied or not by symptoms, to the inability of the virus to mount
a productive replication in the initially inoculated cells. Several genetic factors playing a key role in the success of infection
were identified and their clonings are in progress:
(i) the restriction of long-distance movement of LMV and PPV in the Col accession requires the products of the RTM
genes, up to now believed to be specific to another potyvirus, TEV.
(ii) the restrictions of long-distance movement of LMV and PPV in accession Cvi are controlled by the rlm1 and rpv1
recessive resistance genes respectively, which were mapped in distinct genetic intervals on chromosome 1.
(iii) the symptoms induced by one PPV isolate in accession Ler is controlled by several QTLs mapped in different parts
of the Arabidopsis genome.
To extend this study, a core-collection (24 Arabidopsis accessions) representing 96% of the intra-specific genetic diversity
has been screened by a small panel of PPV and LMV isolates covering the genetic diversity of each virus. This work allowed
to identify new resistance phenotypes as well as situations with generalized symptomatic infections. The involvement of the
corresponding new host genes in the Arabidopsis/potyvirus interactions will be further analysed.
(1) Revers F. et al., 2003. MPMI 16, 608-616.
(2) Decroocq V. et al., 2006.MPMI 19, 541-549.