Abstract
Black leaf streak, caused by the fungus Mycosphaerella fijiensis, is the most important disease affecting the commercial production of banana and plantain in the world. Phenylalanine-ammonia-lyase (PAL) is an enzyme found in a large group of plants, which catalyzes the first reaction in the metabolic pathway of phenylpropanoid compounds. Phenylphenalenons, a type of phenylpropanoid metabolites, have been found in banana and have been suggested to be involved in resistance against pathogens. Thus, PAL might be an important enzyme in the plant-pathogen interaction. In this work, PAL cDNAs were isolated, and sequenced completely or partially, from different banana cultivars such as ‘Calcutta 4’ (Musaacuminata ssp. burmannicoides), ‘Grain Nain’ (AAA, Cavendish subgroup), ‘Yangambi Km5’ (AAA, Ibota subgroup) and ‘Williams’ (AAA, Cavendish subgroup). The obtained sequences were compared, and their secondary and three-dimensional structures of their deduced protein sequences were modeled. Several structural differences between cultivars were found. Additionally, expression analysis showed marked differences in the expression of PAL depending on the cultivar. In particular, PAL from black leaf streak- resistant ‘Calcutta 4’ showed highest expression in the early hours of infection in contrast to the susceptible ‘Williams’ cultivar.
Highlights
Banana and plantain are important crops for staple food and fresh fruit export in the international markets
M. fijiensis infection begins by deposition of spores on the leaf of the banana plant followed by germination within 2-3 hours on the leaf surface provided that a water film is present on the leaf and humidity conditions are appropriate
Complete and partial cDNAs coding for the phenylalanine ammonia-lyase enzyme from two resistant and two susceptible cultivars of Musa acuminata were isolated and characterized
Summary
Banana and plantain are important crops for staple food and fresh fruit export in the international markets. These crops are damaged by several diseases that cause significant losses for farmers (Robinson & Saúco, 2010). The most important and destructive fungal disease is Black leaf streak, caused by Mycosphaerella fijiensis. Cytological studies of the interactions between M. fijiensis, the susceptible genotype Grande Naine, have shown that there is a long period of biotrophy before any necrosis is observed. During this period, little evidence of disease can be seen externally
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