Compounds of Betula Platyphylla Cell Suspension Cultures in Response to Fungal Elicitor

Abstract

ABSTRACTTo determine which triterpenoid compounds respond to fungal elicitors, four oxidosqualene cyclase (OSC) genes involved in triterpenoid biosynthesis, namely, β-amyrin synthase (β-AS), lupeol synthase (LUS), cycloartenol synthase (CAS1 and CAS2), were investigated in cell suspension cultures of Betula platyphylla using real-time quantitative PCR. The results showed that the fungal elicitor significantly increased the mRNA levels of the four OSCs. However, the expression profile of the four studied OSCs in response to fungal elicitation was different; the CAS expression rate was about 50% in the four OSCs after 2 h to 8 h of fungal elicitation, LUS expression was about 70% after 8 h of fungal elicitation, and the LUS mRNA level and its product betulin reached their maxima (18-fold and 2.5-fold that of the control) at 24 h. This result suggests that the lupeol synthase pathway is the major source of triterpenoid production by B. platyphylla cell suspension cultures in response to fungal elicitors. In addition, the activity ofphenylalanine ammonia-lyase (PAL) and peroxidase (POD) in the fungal treated cell cultures increased, reaching their maxima after 6 h of fungal elicitation and then slowly declining thereafter. This result was in accordance with CAS gene expression and in contrast with that of LUS. Therefore, OSCs may have different roles and synergistic interactions in response to fungal elicitation.