Genomes, diversity and resistance gene analogues in Musa species

摘要

Resistance genes (R genes) in plants are abundant and may represent more than 1% of all the genes. Their diversity is critical to the recognition and response to attack trom diverse pathogens. Like many other crops, banana and plantain face attacks from potentially devastating fungal and bacterial diseases, increased by a combination of worldwide spread of pathogens, exploitation of a small number of varieties, new pathogen mutations, and the lack of effective, benign and cheap chemical control. Thechallenge for plant breeders is to identify and exploit genetic resistances to diseases, which is particularly difficult in banana and plantain where the valuable cultivars are sterile, parthenocarpic and mostly triploid so conventional genetic analysisand breeding is impossible. In this paper, we review the nature of R genes and the key motifs, particularly in the Nucleotide Binding Sites (NBS), Leucine Rich Repeat (LRR) gene class. We present data about identity, nature and evolutionary diversity ofthe NBS domains of Musa R genes in diploid wild species with the Musa acuminata (A), M. balbisiana (B), M. schizocarpa (S), M. textilis (T), M. velutina and M. or-nata genomes, and from various cultivated hybrid and trip-loid accessions, using PCR primers to isolate the domains from genomic DNA. Of 135 new sequences, 75% of the sequenced clones had uninterrupted open reading frames (ORFs), andphylogenetic UPGMA tree construction showed four clusters, one from Musa ornata, one largely from the B and T genomes, one from A and M. velutina, and the largest with A, B, T and S genomes. Only genes of the coiled-coil (non-TIR) class were found, typical of the grasses and presumably monocotyledons. The analysis of R genes in cultivated banana and plantain, andtheir wild relatives, has implications for identification and selection of resistance genes within the genus which maybe useful for plant selection and breeding and also for defining relationships and genome evolution patterns within the genus using themulti-copy and variable resistance genes.