THE MAIZE LETHAL-LEAF-SPOT-1 MUTANT HAS ELEVATED RESISTANCE TO FUNGALINFECTION AT THE LEAF EPIDERMIS

The maize lethal leaf spot 1 (lls1) mutant exhibits enhanced resistanc e to fungal pathogens. The lls1 resistance to Cochliobolus heterostrop hus has two components: (i) lesion number is reduced 40% relative to w ild type; and (ii) the lesions that do form often do not contain viabl e fungus, This lesion sterility is dependent upon leaf maturity and li ght, whereas reduced lesion number is not. The lls1 lesions express pa thogenesis-related proteins at high levels, so lesion sterility likely results from activation of defense systems and necrosis, Reduced lesi on number is correlated with a reduction of C. heterostrophus spore ge rmination, hyphal growth, and haustoria formation on the leaf epidermi s, The rust pathogen Puccinia sorghi has reduced pustule formation on lls1, and its germination and growth are also slowed on the epidermis, However, after entering the mesophyll through stomata, P. sorghi can form pustules on lls1, and even green islands within necrotic lls1 les ions, In situ mRNA hybridization shows that Lls1 is predominantly expr essed in the leaf epidermis, coincident with the site of resistance in the mutant.