Interrelation between ABA and phospholipases D, C and A2 in early responses of citrus fruit to Penicillium digitatum infection

Abstract

We investigated whether phospholipases play a role in citrus fruit susceptibility to be infected by Penicillium digitatum, and whether a connection exists between hormone abscisic acid (ABA) and phospholipases in the citrus fruit-P. digitatum interaction. Changes in both the activity of enzymes PLD, PLC and PLA2 and the expression of a set of genes encoding them in response to infection in Navelate (Citrus sinensis (L.) Osbeck) orange and its ABA-deficient mutant Pinalate, which is less resistant to infection, were compared. The results showed the activation of PLD and PLC in infected Navelate fruit before disease development, and this activation was attenuated in the mutant, which suggests that both enzymes play a protective role in citrus fruit to cope with P. digitatum infection and the participation of ABA in their regulation. The transcriptional analyses further demonstrated a differential activation of various phospholipases-encoding genes by the fungus. Of the CsPLD genes (CsPLDα, CsPLDβ, CsPLDδ, CsPLDγ, CsPLDζ), the fungus had a stronger effect on CsPLDγ and CsPLDζ. This is the first report to suggest the participation of a PLDζ isoform in the plant-microbe interaction, and to indicate that this gene may be modulated by ABA in response to infection. The results also revealed that the CsPLC isoforms encoding both non-specific PLC (NPC) and phosphoinositide-specific PLCs (PI-PLC) may participate in the citrus fruit-P. digitatum interaction, and that ABA action occurs upstream of CsPI-PLC gene activation in infected citrus fruit. The changes induced by the fungus in PLA2 activity and gene expression were less relevant.