Studies on Molecular Determinants of Stem Rust in Wheat (Triticum aestivum)

Abstract

Almost 90% of the wheat is facing the threat of stem rust (Puccinia graminis) worldwide. In Pakistan, most of the farmers tend to grow old wheat varieties, which are susceptible to the disease. Replacement of older varieties with high yielding and modern genetically bred varieties will protect farmers against the inevitable attack of stem rust and other diseases. The inevitability of Puccinia graminis f. sp. tritici (Pgt) migration from Iran to Pakistan, coupled with the presence of dangerous new races of yellow rust and leaf rust, are of such importance that their molecular surveillance and rust resistant varieties are now required to improve genetically. Constantly evolving new variants of plant pathogens pose a threat to wheat production. To overcome this, lot of efforts have been made to better understand molecular aspects of resistance to disease and virulence factors that promote the onset of disease. There are many genes identified and characterized, which have resistance against stem rust disease to various levels. They include Sr gene family. Screening of these Sr gene family and some other genes (RPG genes) was done against wheat germplasm. We screened 108 wheat cultivars for different reported resistant genes. Frequency of Sr45 is highest among all other genes which is 65%. Sr35, RPG1 and Sr22 have gene frequency respectively 58%, 37% and 33%. While Sr33 and RPG5 does not appear in any cultivar. Sr22 was selected for isolation and transformation. Today, many transformation methods of resistant genes to various crop plants including wheat are widely used. Sr22 was triggered by inducing Puccinia graminis on healthy resistant varieties such as Mexi-Pak, Auqab 2000 and AS 2002. After inducing Puccinia graminis on healthy plant total mRNA was isolated which was used to synthesize cDNA and full-length gene. The gene was introduced to a commercial susceptible variety, LASANI 2008. Gene gun method was used for transformation. The pCAMBIA2300 plasmid was used having the Kanamycin resistant gene and Cauliflower Mosaic Virus promoter. After transformation, gene integration and expression studies were carried out.