Stage-specific reprogramming of defense responsive genes during Lr24-mediated leaf rust resistance in wheat

Resistance expressed by plants against different rust pathogens is a unique and a very well-coordinated process. The defense responsive genes are the performers of such responses in plants. Understanding the regulation and mechanism of action of these genes is a key constituent of strategic resistance breeding programmes. The present study is aimed at evaluating and comparing the temporal expression pattern of defense responsive genes during early infection phase in compatible and incompatible interactions between wheat and leaf rust to elucidate the molecular basis of Lr24- mediated rust resistance. Lr24 confers resistance to almost all the pathotypes of Puccinia triticina (Pt) reported from Indian subcontinent and Australia. Expression profiles of 10 pathogen responsive genes representing different classes were studied in susceptible (HS240) and resistant (HW2020) wheat near-isogenic lines interacting with Pt. The expression profiles of these genes revealed that the transcript levels of aquaporin, endochitinase, β-1,3-glucanase, Type 1 non-specific lipid transfer protein precursor, phenylalanine ammonia-lyase and caffeic acid O-methyltransferase were significantly higher in incompatible interaction. Relatively higher expression of phenylalanine ammonia-lyase and aquaporin was observed at the pre-haustorial stage [6 h post inoculation (hpi) and 12 hpi], while expression of endo-chitinase and lipid transfer protein was higher during the post-haustorial stage (24 hpi and 48 hpi) in the incompatible interaction. Induced expression of class III peroxidase was maintained throughout pre- and post-haustorial stages in the compatible interaction. The results of the current study could distinguish the defense responsive genes playing a critical role in wheat resistance or susceptibility to leaf rust. We feel that this understanding will allow devising novel strategies to regulate wheat leaf rust pathogen interactions through genetic engineering.