Overexpression of White Collar-1 (WC-1) activates circadian clock-associated genes, but is not sufficient to induce most light-regulated gene expression in Neurospora crassaover-expression of WC-1 show circadian fluctuations in their levels. These data suggest that WC-1 can mediate both light and circadian responses, with an increase in WC-1 levels affecting circadian clockresponsive gene regulation and other features of WC-1, possibly its phosphorylation, affecting lightresponsive gene regulation. IntroductionThe filamentous fungus Neurospora crassa is a model organism for studies of blue-light perception and signal transduction. Blue light regulates several developmental and morphological processes in N. crassa, including the induction of the synthesis of carotenoids in mycelia, the formation of asexual spores and the resetting of the circadian clock. The regulation of these processes occurs primarily at the level of gene expression, and several blue light-regulated genes have been identified (reviewed by Lauter, 1996;Linden et al., 1997). Blue-light responses are abolished in mutations of two genes, white collar-1 (wc-1) and wc-2, demonstrating that the products of these genes function in blue-light signal transduction (Harding and Turner, 1981;Degli-Innocenti and Russo, 1984;Ballario and Macino, 1997).WC-1 and WC-2 are nuclear proteins (Schwerdtfeger and Linden, 2000;Cheng et al., 2001;Denault et al., 2001) that bear sequence similarity to the GATA zinc finger family of transcription factors found in fungi and vertebrates (Ballario et al., 1996;Linden and Macino, 1997). WC complexes bind to consensus GATA elements within the promoters of blue light-regulated genes in N. crassa (Carattoli et al., 1994). Both WC-1 and WC-2 contain PAS domains that are required for the proteins to homodimerize and heterodimerize in vitro and in vivo (Ballario et al., 1996;Cheng et al., 2002). The wc-1 and wc-2 genes are themselves induced by light (Ballario et al., 1996;Linden and Macino, 1997). This induction results in a transient increase in WC-1 protein levels, but little or no change in the levels of WC-2 (Talora et al., 1999;Schwerdtfeger and Linden, 2000). Several experiments have demonstrated that WC-2 is not limiting in cells (Cheng et al., 2001;Denault et al., 2001). WC-2 is always present in the nucleus at levels greatly in excess of SummaryMany processes in fungi are regulated by light, but the molecular mechanisms are not well understood. The White Collar-1 (WC-1) protein is required for all known blue-light responses in Neurospora crassa. In response to light, WC-1 levels increase, and the protein is transiently phosphorylated. To test the hypothesis that the increase in WC-1 levels after light treatment is sufficient to activate light-regulated gene expression, we used microarrays to identify genes that respond to light treatment. We then overexpressed WC-1 in dark-grown tissue and used the microarrays to identify genes regulated by an increase in WC-1 levels. We found that 3% of the genes were responsive to lig...

SUMMARYArabidopsis thaliana contains 18 genes encoding Hsp70s. This heat shock protein superfamily is divided into two sub-families: DnaK and Hsp110/SSE. In order to functionally characterize members of the Hsp70 superfamily, loss-of-function mutants with reduced cytosolic Hsp70 expression were studied. AtHsp70-1 and AtHsp70-2 are constitutively expressed and represent the major cytosolic Hsp70 isoforms under ambient conditions. Analysis of single and double mutants did not reveal any difference compared to wild-type controls. In yeast, SSE protein has been shown to act as a nucleotide exchange factor, essential for Hsp70 function. To test whether members of the Hsp110/SSE sub-family serve essential functions in plants, two members of the sub-family, AtHsp70-14 and AtHsp70-15, were analysed. Both genes are highly homologous and constitutively expressed. Deficiency of AtHsp70-15 but not of AtHsp70-14 led to severe growth retardation. AtHsp70-15-deficient plants were smaller than wild-type and exhibited a slightly different leaf shape. Stomatal closure under ambient conditions and in response to ABA was impaired in the AtHsp70-15 transgenic plants, but ABA-dependent inhibition of germination was not affected. Heat treatment of AtHsp70-15-deficient plants resulted in drastically increased mortality, indicating that AtHsp70-15 plays an essential role during normal growth and in the heat response of Arabidopsis plants. AtHsp70-15-deficient plants are more tolerant to infection by turnip mosaic virus. Comparative transcriptome analysis revealed that AtHsp70-15-deficient plants display a constitutive stress response similar to the cytosolic protein response. Based on these results, AtHsp70-15 is likely to be a key factor in proper folding of cytosolic proteins, and may function as nucleotide exchange factor as proposed for yeast.

SUMMARYPost-transcriptional gene silencing often limits the over-expression of transgenes in transgenic plants. It involves RNA-DEPENDENT RNA POLYMERASE 6 (RDR6), which recognizes aberrant transcripts, such as inaccurately processed or uncapped mRNA, and triggers silencing of target transcripts. Here, we describe the isolation and characterization of an Arabidopsis mutant displaying increased transgene silencing (its1). Reduced accumulation of transgene mRNA in the its1 mutant background was accompanied by accumulation of transgene-specific siRNAs and was overcome by potyvirus infection. We therefore speculated that ITS1 is a suppressor of post-transcriptional gene silencing. Map-based cloning and subsequent complementation revealed that ITS1 encodes DECAPPING 2 (DCP2), which is crucial for decapping, a prerequisite for mRNA degradation. In agreement with the proposed function of DCP2, we found a reduced accumulation of uncapped mRNA in the its1 mutant. Furthermore, silencing in the its1 mutant was dependent on RDR6 function, suggesting that reduced decapping leads to accumulation of aberrant capped mRNA. Hence, we provide evidence for a class of aberrant mRNA that accumulates upon impaired mRNA decapping and triggers posttranscriptional gene silencing in Arabidopsis. As DCP2 knockouts cause post-embryo lethality, we isolated a hypomorphic dcp2 allele, providing insights into mRNA degradation and its interplay with post-transcriptional gene silencing.

195 Identifi cation of a residue responsible for UDP-sugar donor selectivity of a dihydroxybenzoic acid glycosyltransferase from Arabidopsis natural accessions. H.-Y. Chen and X. Li 204 PYK10 myrosinase reveals a functional coordination between endoplasmic reticulum bodies and glucosinolates in Arabidopsis thaliana. R.T. Nakano, M. Pis´lewskaPis´lewska-Bednarek, K. Yamada, P.P. Edger, M. Miyahara, M. Kondo, C. Böttcher, M. Mori, M. Nishimura, P. Schulze-Lefert, I. Hara-Nishimura and P. Bednarek 221 Identifi cation and characterization of a plastidial phosphatidylglycerophosphate phosphatase in Arabidopsis thaliana. Y. Zhou, G. Hölzl, K. vom Dorp, H. Peisker, M. Melzer, M. Frentzen and P. Dörmann 235 CENH3 morphogenesis reveals dynamic centromere associations during synaptonemal complex formation and the progression through male meiosis in hexaploid wheat. A. Sepsi, J.D. Higgins, J.S.(Pat). Heslop-Harrison and T. Schwarzacher 250 IDL6-HAE/HSL2 impacts pectin degradation and resistance to Pseudomonas syringae pv tomato DC3000 in Arabidopsis leaves. X 264 Differential deposition of H2A.Z in combination with histone modifi cations within related genes in Oryza sativa callus and seedling. 354 ABI4 represses the expression of type-A ARRs to inhibit seed germination in Arabidopsis. X. Huang, X. Zhang, Z. Gong, S. Yang and Y. Shi 366 Genetic variation of growth dynamics in maize (Zea mays L.) revealed through automated non-invasive phenotyping. 407 Investigating the mechanisms of glyphosate resistance in goosegrass (Eleusine indica (L.) Gaertn.) by RNA sequencing technology .

Many plant viruses encode for specialized movement proteins (MP) to facilitate passage of viral material to and through plasmodesmata (PD). To analyze intracellular trafficking of potato leaf roll virus (PLRV) movement protein (MP17) we performed GFP fusion experiments with distinct deletion variants of MP17. These studies revealed that the C-terminus of MP17 is essential but not sufficient for PD targeting. Interestingly, fusion of GFP to three C-terminal MP17 deletion variants resulted in the accumulation of GFP in chloroplasts. This indicates that MP17 harbors hidden plastid targeting sequences. Previous studies showed that posttranslational protein phosphorylation influences PD targeting of MP and virus spread. Analysis of MP17-derived phospho-peptides by mass spectrometry revealed four phosphorylated serine residues (S71, S79, S137, and S140). Site-directed mutagenesis of S71/S79 and S137/S140 showed that the C-terminal serine residues S137/S140 are dispensable for PD targeting. However, exchange of S71/S79 to A71/A79 abolished PD targeting of the mutated MP17 protein. To mimic phosphorylation of S71/S79 both amino acids were substituted by aspartic acid. The resulting D71/D79 variant of MP17 was efficiently targeted to PD. Further deletion analysis showed that PD targeting of MP17 is dependent on the C-terminus, phosphorylation of S71 and/or S79 and a N-terminal domain.