Identification and mapping of an AFLP marker linked to Gm7, a gall midge resistance gene and its conversion to a SCAR marker for its utility in marker aided selection in rice

We have identified an AFLP marker SA598 that is linked to Gm7, a gene conferring resistance to biotypes 1, 2 and 4 of the gall midge ( Orseolia oryzae), a major dipteran pest of rice. A set of PCR primers specific to an RFLP marker, previously identified to be linked to another gall midge resistance gene Gm2, also amplified a 1.5-kb (F8LB) fragment that is linked to Gm7. Gm7 is a dominant gene and non-allelic to Gm2. Hybridization experiments with clones from a YAC library of Nipponbare, a japonica variety, a BAC library of IR-BB21, an indica variety, and cosmid clones encompassing Gm2 from Phalguna, an indica variety, with F8LB and SA598 as probes, revealed that Gm7 is tightly linked to Gm2 and is located on chromosome 4 of rice. SA598 was sequenced and the sequence information was used to design sequence-characterized amplified region (SCAR) primers. The potential use of these SCAR primers in marker-aided selection of Gm7 in a rice breeding program has been demonstrated.     

A Bkm-associated human y-chromosomal DNA is conserved and transcribed in the testis of mouse

Y chromosome associated genes and repetitive sequences are continually viewed from the point of view of their possible involvement in sex determination and in the evolution of such a mechanism, thus sustaining an interest in the identification of novel sequences to gain newer insights. Here we have used the highly conserved class of Bkm repeats to isolate its associated sequences from the Y chromosome under the assumption that these sequences could be involved in sex determination and might also reflect the evolutionary status of the Y chromosome. Towards this end we have screened a genomic library enriched with human Y chromosome DNA with Bkm. One of the positive clones, C65, has a pericentromeric location on the Y chromosome and is present in a number of human sex-reversed XX males. The 10.5 kb insert of clone C65 has been further subcloned (pFI, pFII, pFIII, pFIV). The subclone pFIII is present in both sexes in human and mouse, whereas pFIV is primate specific and present in both sexes. pFII contains sequences homologous to Bkm. pFI is conserved in mouse and man, but is Y specific only in primates. Although present in both sexes in mouse, pFI is transcribed specifically in the male testis suggesting that it may be involved in the process of sex determination or testis differentiation and spermatogenesis.     

Isolation and FISH mapping of Yeast Artificial Chromosomes (YACs) encompassing an allele of the Gm2 gene for gall midge resistance in rice

 Ten yeast artificial chromosomes (YACs) spanning the Gm2 locus have been isolated by screening high-density filters containing a total of approximately 7000 YAC (representing six genome equivalents) clones derived from a japonica rice, Nipponbare. The screening was done with five RFLP markers flanking a gall midge resistance gene, Gm2, which was previously mapped onto chromosome 4 of rice. This gene confers resistance to biotype 1 and 2 of gall midge (Orseolia oryzae), a major insect pest of rice in South and Southeast Asia. The RFLP markers RG214, RG329 and F8 hybridized with YAC Y2165. Two overlapping YAC clones (Y5212 and Y2165) were identified by Southern hybridization, with Gm2-flanking RFLP markers, and their inserts isolated. The purified YACs and RFLP markers flanking Gm2 were labeled and physically mapped by the fluorescence in situ hybridization (FISH) technique. All of them mapped to the long arm of chromosome 4 of the resistant variety of rice, ‘Phalguna’, confirming the previous RFLP mapping data. Received: 15 December 1997 / Accepted: 5 March 1998     

Genetic,physiological and molecular interactions of rice and its major dipteran pest,gall midge

The gall midge, Orseolia oryzae, is a major dipteran pest of rice affecting most rice growing regions in Asia, Southeast Asia and Africa. Chemical and other cultural methods for control of this pest are neither very effective nor environmentally safe. The gall midge problem is further compounded by the fact that there are many biotypes of this insect and new biotypes are continuously evolving. However, resistance to this pest is found in the rice germ plasm. Resistance is generally governed by single dominant genes and a number of non-allelic resistance genes that confer resistance to different biotypes have been identified. Genetic studies have revealed that there is a gene-for-gene interaction between the different biotypes of gall midge and the various resistance genes found in rice. This review discusses different aspects of the process of infestation by the rice gall midge and its interaction with its host. Identification of the gall midge biotypes by conventional methods is a long and tedious process. The review discusses the PCR-based molecular markers that have been developed recently to speed up the identification process. Similarly, molecular markers have been developed for two gall midge resistance genes in rice – Gm2 and Gm4t – and these markers are now being used for marker-assisted selection. The mapping, tagging and map-based gene cloning of one of these genes – Gm2 – has also been discussed. This revised version was published online in June 2006 with corrections to the Cover Date.