Molecular cloning and characterization of the AVR-Pia locus from a Japanese field isolate of Magnaporthe oryzae.

In order to clone and analyse the avirulence gene AVR-Pia from Japanese field isolates of Magnaporthe oryzae, a mutant of the M. oryzae strain Ina168 was isolated. This mutant, which was named Ina168m95-1, gained virulence towards the rice cultivar Aichi-asahi, which contains the resistance gene Pia. A DNA fragment (named PM01) that was deleted in the mutant and that co-segregated with avirulence towards Aichi-asahi was isolated. Three cosmid clones that included the regions that flanked PM01 were isolated from a genomic DNA library. One of these clones (46F3) complemented the mutant phenotype, which indicated clearly that this clone contained the avirulence gene AVR-Pia. Clone 46F3 contained insertions of transposable elements. The 46F3 insert was divided into fragments I-VI, and these were cloned individually into a hygromycin-resistant vector for the transformation of the mutant Ina168m95-1. An inoculation assay of the transformants revealed that fragment V (3.5 kb) contained AVR-Pia. By deletion analysis of fragment V, AVR-Pia was localized to an 1199-bp DNA fragment, which included a 255-bp open reading frame with weak homology to a bacterial cytochrome-c-like protein. Restriction fragment length polymorphism analysis of this region revealed that this DNA sequence co-segregated with the AVR-Pia locus in a genetic map that was constructed using Chinese isolates

Suppression of a Phospholipase D Gene, OsPLDβ1, Activates Defense Responses and Increases Disease Resistance in Rice1[C][W][OA]

Phospholipase D (PLD) plays an important role in plants, including responses to abiotic as well as biotic stresses. A survey of the rice (Oryza sativa) genome database indicated the presence of 17 PLD genes in the genome, among which OsPLDα1, OsPLDα5, and OsPLDβ1 were highly expressed in most tissues studied. To examine the physiological function of PLD in rice, we made knockdown plants for each PLD isoform by introducing gene-specific RNA interference constructs. One of them, OsPLDβ1-knockdown plants, showed the accumulation of reactive oxygen species in the absence of pathogen infection. Reverse transcription-polymerase chain reaction and DNA microarray analyses revealed that the knockdown of OsPLDβ1 resulted in the up-/down-regulation of more than 1,400 genes, including the induction of defense-related genes such as pathogenesis-related protein genes and WRKY/ERF family transcription factor genes. Hypersensitive response-like cell death and phytoalexin production were also observed at a later phase of growth in the OsPLDβ1-knockdown plants. These results indicated that the OsPLDβ1-knockdown plants spontaneously activated the defense responses in the absence of pathogen infection. Furthermore, the OsPLDβ1-knockdown plants exhibited increased resistance to the infection of major pathogens of rice, Pyricularia grisea and Xanthomonas oryzae pv oryzae. These results suggested that OsPLDβ1 functions as a negative regulator of defense responses and disease resistance in rice

SSR遺伝子型を用いた圃場のいもち病菌の拡散の評価

農家水田圃場において，一作期内でのいもち病菌の拡散程度および発病への影響程度を推定するために，SSR マーカーを用いて圃場分離菌株を識別し，伝染源に由来するいもち病菌が検出される距離と検出頻度を調査した．2 箇所の伝染源がある8 筆の圃場について，伝染源からの距離と葉および穂いもち発病程度を調査した結果，伝染源由来と考えられる発病は，葉いもちでおおむね50 m，穂いもちでは10～80 m（方向により異なる）の距離以内で発病が見られ，発病程度は伝染源から遠くなるほど低下した．また，伝染源を構成する主要SSR 遺伝子型菌株検出割合と伝染源からの距離と発病程度の関係から，葉および穂いもちともに伝染源から約100 m までは伝染源由来の菌が拡散し，50 m 以内では発病程度に対する影響が大きいことが明らかとなった．いもち病菌集団を農家別に分けてペアワイズRST を計算したところ，2 箇所の伝染源からの相互の遺伝子流動により，葉いもち集団間に比較して穂いもち集団間での遺伝的距離の方が小さくなる傾向を示した