Submitted to: Genome Research
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/27/2002
Publication Date: 12/2/2002
Citation: Interpretive Summary: Cereal crops feed the majority of the world¿s ever-growing population. Disease resistance genes (R genes) are one important tool used by these plants to defend against pathogen attack. Resistance genes and the proteins they make act as the plant¿s early warning system by detecting invading pathogens and initiating a defense response to stop or slow the spread of the invading pest. The largest group of these disease resistance genes is named the nucleotide binding site-leucine-rich repeat (NBS-LRR) gene class. In this paper NBS-LRR genes from rice were compared, both in structure and number, to other cereals plant species and to the model plant Arabidopsis. A more thorough understanding of these genes and their evolution may allow scientists to develop durable disease resistant plants by identifying, isolating, and transferring functional genes from one plant species to another. Over 354 NBS-LRR gene families were identified from rice from over1080 DNA sequences by using computer software that groups sequences based on their relatedness. One novel NBS gene class was identified during this work.
Technical Abstract: The diversity of the largest group of plant disease resistance genes, the nucleotide binding site-leucine-rich repeat (NBS-LRR) genes, was examined in cereals following polymerase chain reaction (PCR) cloning and database mining. NBS-LRR genes in rice are a large and diverse class with more than 600 genes, at least three to four times the complement of Arabidopsis. Most occur in small families containing one or a few cross-hybridizing members. Unlike in Arabidopsis and other dicots, the class of NBS-LRR genes coding for a Toll and mammalian interleukin-1 receptor (TIR) domain were not amplified during the evolution of the cereals. Genes coding for TIR domains are present in the rice genome, but have diverged from the NBS-LRR genes. Most cereal genes are similar in structure to the members of the non-TIR class of dicots, although many do not code for a coiled-coil domain in their amino termini. One unique class of cereal genes, with ~50 members, codes for proteins similar to the N-termini and NBS domains of resistance genes but does not code for LRR domains. The resistance gene repertoire of grasses has changed from that of dicots in their independent evolution since the two groups diverged. It is not clear whether this reflects a difference in downstream defense signaling pathways.