PECTIN ACETYLESTERASE9 Affects the Transcriptome and Metabolome and Delays Aphid Feeding.

The plant cell wall plays an important role in damage-associated molecular pattern (DAMP)-induced resistance to pathogens and herbivorous insects. Our current understanding of cell wall-mediated resistance is largely based on the degree of pectin methylesterification. However, little is known about the role of pectin acetylesterification in plant immunity. This study describes how one pectin-modifying enzyme, PECTIN ACETYLESTERASE 9 (PAE9), affects the Arabidopsis thaliana transcriptome, secondary metabolome and aphid performance. Electro-penetration graphs showed that Myzus persicae aphids established phloem feeding earlier on pae9 mutants. Whole-genome transcriptome analysis revealed a set of 56 differentially expressed genes (DEGs) between uninfested pae9-2 mutants and wild-type plants. The majority of the DEGs were enriched for biotic stress responses and downregulated in the pae9-2 mutant, including PAD3 and IGMT2, involved in camalexin and indole glucosinolate biosynthesis, respectively. Relative quantification of more than 100 secondary metabolites revealed decreased levels of several compounds, , including camalexin and oxylipins, in two independent pae9 mutants. In addition, absolute quantification of phytohormones showed that jasmonic acid (JA), JA-isoleucine, salicylic acid, abscisic acid, and indole-3-acetic acid were compromised due to PAE9 loss of function. After aphid infestation, however, pae9 mutants increased their levels of camalexin, glucosinolates and JA, and no long-term effects were observed on aphid fitness. Overall, these data show that PAE9 is required for constitutive upregulation of defense-related compounds, but that it is not required for aphid-induced defenses. The signatures of phenolic antioxidants, phytoprostanes and oxidative stress-related transcripts indicate that the processes underlying PAE9 activity involve oxidation-reduction reactions.