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Summary Nitric oxide (NO) is an important signaling compound in prokaryotes and eukaryotes. In plants, NO regulates critical developmental transitions and stress responses. Here, we identify a mechanism for NO sensing that coordinates responses throughout development based on targeted degradation of plant-specific transcriptional regulators, the group VII ethylene response factors (ERFs). We show that the N-end rule pathway of targeted proteolysis targets these proteins for destruction in the presence of NO, and we establish them as critical regulators of diverse NO-regulated processes, including seed germination, stomatal closure, and hypocotyl elongation. Furthermore, we define the molecular mechanism for NO control of germination and crosstalk with abscisic acid (ABA) signaling through ERF-regulated expression of ABSCISIC ACID INSENSITIVE5 (ABI5). Our work demonstrates how NO sensing is integrated across multiple physiological processes by direct modulation of transcription factor stability and identifies group VII ERFs as central hubs for the perception of gaseous signals in plants., Graphical Abstract, Highlights • We elucidate a general molecular mechanism for nitric oxide sensing in plants • Group VII ERFs act as nitric oxide sensors via the N-end rule pathway • Group VII ERFs are shown to mediate crosstalk between nitric oxide and abscisic acid • The N-end rule regulates nitric oxide homeostasis through group VII ERFs, Gibbs et al. report that NO-dependent degradation of group VII ERF transcription factors by the N-end rule pathway mediates NO sensing and signal transduction, identifying these transcription factors as central hubs for the perception of gaseous signals in plants.

In Peronospora parasitica (At) (downy mildew), the genetic determinants of cultivar-specific recognition by Arabidopsis thaliana are the Arabidopsis thaliana-recognised (ATR) avirulence genes. We describe the identification of 10 amplified fragment length polymorphism (AFLP) markers that define a genetic mapping interval for the ATR1Nd avirulence allele, the presence of which is perceived by the RPP1Nd resistance gene. Furthermore, we have constructed a P. parasitica (At) bacterial artificial chromosome (BAC) library comprising over 630 Mb of cloned DNA. We have isolated 16 overlapping clones from the BAC library that form a contig spanning the genetic interval. BAC sequence-derived markers and a total mapping population of 311 F2 individuals were used to refine the ATR1Nd locus to a 1 cM interval that is represented by four BAC clones and spans less than 250 kb of DNA. This work demonstrates that map-based cloning techniques are feasible in this organism and provides the critical foundations for cloning ATR1Nd using such a strategy.

Amplified fragment length polymorphism (AFLP) fingerprints and internal transcribed spacer 1 (ITS1) sequences from 27 Peronospora parasitica isolates (collected from Arabidopsis thaliana or Brassica oleracea), 5 Albugo candida isolates (from the same hosts and from Capsella bursa-pastoris), and 1 Bremia lactucae isolate (from Lactuca sativa) were compared. The AFLP analysis divided the isolates into five groups that correlated with taxonomic species and, in most cases, with host origin. The only exception was a group consisting of A. candida isolates from both B. oleracea and C. bursa-pastoris. ITS1 sequence analysis divided the isolates into the same five groups, demonstrated the divergence between P. parasitica isolates from A. thaliana and B. oleracea, and, using previously published ITS1 sequences, clearly showed the relationship between A. candida isolates from different hosts.

GARNet, the Genomic Arabidopsis Resource Network, was created to establish UK-based facilities for functional genomic research on Arabidopsis thaliana. In addition, GARNet provides a platform for international Arabidopsis research and for research on other plant species. To use the GARNet facilities apply via the website: http://garnet.arabidopsis.org.uk. All GARNet services and resources are publicly available, and data created using the GARNet resources will be freely distributed via databases held at the Nottingham Arabidopsis Stock Centre and the John Innes Centre.

We have determined the precise point of transcription initiation for five nif (nitrogen fixation) operons of Klebsiella pneumoniae and sequenced the promoters. Our results show that nifF is transcribed in the opposite direction to that previously proposed for nif genes, that nifM is transcribed from two promoters, and that there is a promoter preceding nifU but not nifX, and we present a revised map of nif transcripts. The nif promoters have a characteristic structure of 26 bp located between positions--1 and --26 upstream of the site of transcription initiation: CTGG..8bp...TTGCA...9bp...Py(+1). This structure, which has two regions of conserved sequence, shows no homology to the "consensus promoter" of enteric bacteria. Our results suggest that the--10 homology is equivalent to a "Pribnow box" for promoters expressed under nitrogen-starved conditions and that the--23 homology confers activator specificity on the nif promoters.