The Wheat Puroindoline Genes Confer Fungal Resistance in Transgenic Corn

Puroindoline a and b (Pina and Pinb), together make up the functional components of the wheat grain hardness locus (Ha) and have antimicrobial properties. The antifungal activity of puroindoline proteins, PINA and PINB, has been demonstrated in vitro and in vivo. In this study, Pina and Pinb were introduced into corn under the control of a corn Ubiquitin promoter. Two Pina⁄Pinb expression–positive transgenic events were evaluated for resistance to Cochliobolus heterostrophus, the corn southern leaf blight (SLB) pathogen. Transgenic corn expressing Pins showed significantly increased tolerance to C. heterostrophus, averaging 42.1% reduction in symptoms. Pins are effective in vivo as antifungal proteins and could be valuable tools in corn SLB control. Introduction The puroindolines, Puroindoline a and b (Pina and Pinb), are the functional components of the wheat grain hardness locus (Ha) and control wheat kernel texture (Giroux and Morris 1998). The antifungal activity of PINs has been demonstrated in vitro against several fungal plant pathogens (Dubreil et al. 1998) and in vivo in transgenic rice (Krishnamurthy et al. 2001), apple (Faize et al. 2004) and wheat (Luo et al. 2007). Corn southern leaf blight (SLB), caused by the necrotrophic ascomycete Cochliobolus heterostrophus (Drechs.) Drechs. (anamorph = Bipolaris maydis (Nisikado) Shoemaker; synonym = Helminthosporium maydis Nisikado), is a serious foliar disease frequently found in warm and humid, corn-growing areas worldwide (White 1999). Race O of C. heterostrophus is the most common and predominant race in the United States and has the potential to decrease yield by 40% or more (Byrnes et al. 1989). Most SLB genetic resistance is quantitatively inherited, and the gene action is primarily additive or partially dominant and most U.S. germplasm is largely SLB resistant (Balint-Kurti et al. 2006, 2007, 2008). B73 is a historically important inbred line with high susceptibility to SLB (Carson et al. 2004). Corn does not naturally contain any Pins (Zhang et al. 2009). Both Pina and Pinb were introduced into HiII line, which is a hybrid created between the SLB susceptible inbreds A188 and B73 (Armstrong et al. 1991), and the resulting transgenic lines were backcrossed to B73 and their progeny lines were tested for SLB resistance. Materials and Methods