PROTEIN EXPRESSION PROFILING ASSOCIATED TO BIOTIC STRESS IN MAIZE.

Plant biotic stresses are caused by pathogens, parasites, predators and their outcome results from interaction between, host, pathogen and environment. Pathogens attack could be due by several organisms as fungi, bacteria, viruses oomycetes, nematodes and insects that cause specific and systemic response. Two of the major pests affecting maize crop in Lombardy region are Fusarium verticillioides fungus and the Diabrotica virgifera virgifera LeConte insect. The etiology of two diseases is strictly interdependent, plant fungus infection is often deriving after kernel injuries by wounding or insect attack. F. veritillioides infection typically occurs on kernels, with a high level of fungal infection and micotoxin contamination. In resistant inbred maize genotype, kernel showed significant decrease of infection incidence, with limited amounts of total fumonisin content and reduced fungal growth. We attempt to identify protein involved in Fusarium resistance by protein profile resistant and susceptible lines. We found only two protein peaks at 5.79 and 14.96 Kda that were commonly expressed in the susceptible lines but no specific protein of interest were present in kernel from resistance lines. Only the susceptible line CO354, showed variation in the Late Embryogenesis Abundant LEA3 protein, previously described as protein associated to fungal resistance in maize. D. virgifera attack is prevalentely due by direct larvae infestation and damage to the maize root system. Plants respond to insect infestation by emitting volatile compounds among which the sequiterpene (E)-β-caryophillene that attracts natural enthomopathogenic nematodes. This volatile compound has been found in response to herbivore damage in several wild relatives of maize and in cultivated maize lines from European breeding programs but not in most lines from the North American breeding program. In order to understand mechanisms involved in defence response, maize lines that differ in (E)-β-caryophillene synthase expression were characterized by protein profiling and tps23 gene expression. We found that maize responds to methyl jasmonate treatment and D. virgifera infestation similarly by inducing the tps23 gene, but the jasmonate mediated response differs quantitative and temporary in different maize lines. Methyl jasmonate treatment induce also the expression of other three proteins i.e. actin-depolymerizing factor 3 ADF3, nucleotide pyrophosphatase/phosphodiesterase NPP and anionic peroxidase probably involved in maize herbivore insect response. Proteomic characterization of maize lines differing in response to pathogen attack may be a useful approach to better understand mechanisms involved in plant pathogen response and to find new markers associated to biotic stress response. The potential uses of these biomarkers in assisted breeding program however remain still under investigation.