EIN2-mediated signaling is involved in pre-invasion defense in <i>Nicotiana benthamiana</i> against potato late blight pathogen, <i>Phytophthora infestans</i>

<p><i>Nicotiana benthamiana</i> ABCG1 and ABCG2 are ABC transporters which are probably involved in the export of capsidiol, the major phytoalexin of <i>Nicotiana</i> species. While capsidiol export by these transporters plays an essential role in post-invasion defense against <i>Phytophthora infestans</i>, they also export unidentified antimicrobial compound(s) involved in pre-invasion defense. In this study, promoter activity of <i>NbABCG2</i> (P<i>abcg2a</i>) was analyzed using a <i>GFP</i> marker. Expression of <i>GFP</i> under the control of P<i>abcg2a</i> was significantly increased by co-expression with the INF1 elicitor from <i>P. infestans</i>. Disruption of the ethylene-responsive GCC box in P<i>abcg2a</i> compromised INF1-induced activation of P<i>abcg2a</i>. Consistently, penetration by <i>P. infestans</i> was increased by gene-silencing of <i>NbEIN2</i>, the key ethylene-signaling component, suggesting the involvement of ethylene for pre-invasion defense of <i>N. benthamiana</i>.</p>