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The tomato (Lycopersicon esculentum) Cf-9 resistance gene encodes the first characterized member of the plant receptor-like protein (RLP) family. Other RLPs such as CLAVATA2 and TOO MANY MOUTHS are known to regulate development. The domain structure of RLPs consists of extracellular leucine-rich repeats, a transmembrane helix, and a short cytoplasmic region. Here, we identify 90 RLPs in rice (Oryza sativa) and compare them with functionally characterized RLPs from different plant species and with 56 Arabidopsis (Arabidopsis thaliana) RLPs, including the downy mildew resistance protein RPP27. Many RLPs cluster into four distinct superclades, three of which include RLPs known to be involved in plant defense. Sequence comparisons reveal diagnostic amino acid residues that may specify different molecular functions in different RLP subtypes. This analysis of rice RLPs thus identified at least 73 candidate resistance genes and four genes potentially involved in development. Due to the synteny between rice and other Gramineae, this analysis should provide valuable tools for experimental studies in rice and other cereals.

The tomato (Lycopersicon esculentum) Cf-9 resistance gene encodes the first characterized member of the plant receptor-like protein (RLP) family. Other RLPs such as CLAVATA2 and TOO MANY MOUTHS are known to regulate development. The domain structure of RLPs consists of extracellular leucine-rich repeats, a transmembrane helix, and a short cytoplasmic region. Here, we identify 90 RLPs in rice (Oryza sativa) and compare them with functionally characterized RLPs from different plant species and with 56 Arabidopsis (Arabidopsis thaliana) RLPs, including the downy mildew resistance protein RPP27. Many RLPs cluster into four distinct superclades, three of which include RLPs known to be involved in plant defense. Sequence comparisons reveal diagnostic amino acid residues that may specify different molecular functions in different RLP subtypes. This analysis of rice RLPs thus identified at least 73 candidate resistance genes and four genes potentially involved in development. Due to the synteny between rice and other Gramineae, this analysis should provide valuable tools for experimental studies in rice and other cereals.

A 2.91-billion base pair (bp) consensus sequence of the euchromatic portion of the human genome was generated by the whole-genome shotgun sequencing method. The 14.8-billion bp DNA sequence was generated over 9 months from 27,271,853 high-quality sequence reads (5.11-fold coverage of the genome) from both ends of plasmid clones made from the DNA of five individuals. Two assembly strategies—a whole-genome assembly and a regional chromosome assembly—were used, each combining sequence data from Celera and the publicly funded genome effort. The public data were shredded into 550-bp segments to create a 2.9-fold coverage of those genome regions that had been sequenced, without including biases inherent in the cloning and assembly procedure used by the publicly funded group. This brought the effective coverage in the assemblies to eightfold, reducing the number and size of gaps in the final assembly over what would be obtained with 5.11-fold coverage. The two assembly strategies yielded very similar results that largely agree with independent mapping data. The assemblies effectively cover the euchromatic regions of the human chromosomes. More than 90% of the genome is in scaffold assemblies of 100,000 bp or more, and 25% of the genome is in scaffolds of 10 million bp or larger. Analysis of the genome sequence revealed 26,588 protein-encoding transcripts for which there was strong corroborating evidence and an additional ∼12,000 computationally derived genes with mouse matches or other weak supporting evidence. Although gene-dense clusters are obvious, almost half the genes are dispersed in low G+C sequence separated by large tracts of apparently noncoding sequence. Only 1.1% of the genome is spanned by exons, whereas 24% is in introns, with 75% of the genome being intergenic DNA. Duplications of segmental blocks, ranging in size up to chromosomal lengths, are abundant throughout the genome and reveal a complex evolutionary history. Comparative genomic analysis indicates vertebrate expansions of genes associated with neuronal function, with tissue-specific developmental regulation, and with the hemostasis and immune systems. DNA sequence comparisons between the consensus sequence and publicly funded genome data provided locations of 2.1 million single-nucleotide polymorphisms (SNPs). A random pair of human haploid genomes differed at a rate of 1 bp per 1250 on average, but there was marked heterogeneity in the level of polymorphism across the genome. Less than 1% of all SNPs resulted in variation in proteins, but the task of determining which SNPs have functional consequences remains an open challenge.

Tomato (Lycopersicon esculentum) Cf genes confer resistance to the fungal pathogen Cladosporium fulvum through recognition of secreted avirulence (Avr) peptides. Plant defense responses, including rapid alterations in gene expression, are immediately activated upon perception of the pathogen. Previously, we identified a collection of Avr9/Cf-9 rapidly (15 to 30 min) elicited (ACRE) genes from tobacco (Nicotiana tabacum). Many of the ACRE genes encode putative signaling components and thus may play pivotal roles in the initial development of the defense response. To assess the requirement of 42 of these genes in the hypersensitive response (HR) induced by Cf-9/Avr9 or by Cf-4/Avr4, we used virus-induced gene silencing (VIGS) in N. benthamiana. Three genes were identified that when silenced compromised the Cf-mediated HR. We further characterized one of these genes, which encodes a Ser/Thr protein kinase called Avr9/Cf-9 induced kinase 1 (ACIK1). ACIK1 mRNA was rapidly upregulated in tobacco and tomato upon elicitation by Avr9 and by wounding. Silencing of ACIK1 in tobacco resulted in a reduced HR that correlated with loss of ACIK1 transcript. Importantly, ACIK1 was found to be required for Cf-9/Avr9- and Cf-4/Avr4-mediated HRs but not for the HR or resistance mediated by other resistance/Avr systems, such as Pto/AvrPto, Rx/Potato virus X, or N/Tobacco mosaic virus. Moreover, VIGS of LeACIK1 in tomato decreased Cf-9-mediated resistance to C. fulvum, showing the importance of ACIK1 in disease resistance.