Abstract
Plant cell walls, which are mainly composed of pectin, play important roles in plant defence responses to pathogens. Pectin is synthesised in a highly esterified form and then de-esterified by pectin methylesterases (PMEs). Because of this, PMEs are directly involved in plant defence. However, the molecular mechanisms of their interactions with pectins remain unclear. In this study, we compared the expression level and enzyme activities of PMEs in a banana Cavendish cultivar (Musa AAA ‘Brazilian’) inoculated with Fusarium oxysporum f. sp. cubense pathogenic races 1 (Foc1) and 4 (Foc4). We further examined the spatial distribution of PMEs and five individual homogalacturonans (HGs) with different degree of pectin methylesterification (DM). Results suggested that the banana roots infected with Foc1 showed lower PME activity than those infected with Foc4, which was consisted with observed higher level of pectin DM. The level of HGs crosslinked with Ca2+ was significantly higher in roots infected with Foc1 compared with those infected with Foc4. Therefore, banana exhibited significantly different responses to Foc1 and Foc4 infection, and these results suggest differences in PME activities, DM of pectin and Ca2+-bridged HG production. These differences could have resulted in observed differences in virulence between Foc1 and Foc4.
Highlights
Fusarium oxysporum f. sp. cubense (Foc), the causal agent of banana Fusarium wilt, can cause severe losses in yield and quality
The degree of methylesterfication (DM) of the roots infected with Foc[1] represented an almost 3-fold difference in the DM of roots inoculated with Foc[4]
pectin methylesterases (PMEs) are related to the location of the pectin in the cell wall[30], and they may play an important role in the development of disease
Summary
Fusarium oxysporum f. sp. cubense (Foc), the causal agent of banana Fusarium wilt, can cause severe losses in yield and quality. Foc race 4 (Foc4) causes disease to most commercially grown ‘Cavendish’ banana cultivars (Musa spp., AAA-group), as well as the hosts of Foc[1] and Foc[2]. During the interaction between plant and pathogen, the specific roles of PMEs and molecular mechanisms of PMEs action on pectin remain unclear, and conflicting results were occasionally reported about the level of PME expression[5,13], and changes in cell wall composition[14,15] that occurs when different plants species are infected by different pathogens. There was a report that the spatial distributions of PMEs and different pectin DM affect susceptibility of different banana cultivars to Foc[424]. Whether and how PMEs affect differences in observed virulence between pathogen races remains unclear
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