Expression profiles of genes for enzymes involved in capsidiol production in Nicotiana benthamiana

概要

In Solanaceae plants, the major phytoalexins produced during the induction of plant defense are sesquiterpenoids, such as capsidiol for Nicotiana species and rishitin for Solanum species, which are produced via the mevalonate (MVA) pathway. Eight enzymes are involved in the production of farnesyl pyrophosphate (FPP), the common precursor of phytosterols for maintaining membrane integrity and sesquiterpenoid phytoalexins for plant defense. In this study, expression profiles of N. benthamiana genes for the production of capsidiol during the induction of disease resistance were investigated. In the genome of N. benthamiana, multiple copies of genes for each enzyme in the MVA pathway were identified, and the expression of some, but not all MVA genes, was significantly upregulated after inoculation with Phytophthora infestans, or treatment with the INF1 elicitor, a secretory protein of P. infestans. For genes encoding enzymes involved in capsidiol production, 10 copies of 5-epi-aristolochene synthase (NbEAS) and six copies of 5-epi-aristolochene dihydroxylase (NbEAH) were identified, and all copies were significantly upregulated during the induction of disease resistance. Gene silencing of MAP kinase genes NbWIPK, NbSIPK, and NbNTF4 compromised INF1-induced production of phytoalexins. Expression analysis of control and NbWIPK/SIPK/NTF4-silenced plants indicated that most of the MVA genes are not under the control of these MAP kinases. In contrast, the expression pattern of NbWIPK/SIPK/NTF4 and all copies of NbEAH genes showed significant correlation, suggesting that MAP kinases are critical regulators of transcriptional upregulation of specific genes for capsidiol production.

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