A Novel Transcription Factor CaSBP12 Gene Negatively Regulates the Defense Response against Phytophthora capsici in Pepper (Capsicum annuum L.)

Abstract

SBP-box (Squamosa-promoter binding protein) genes are a type of plant-specific transcription factor and play important roles in plant growth, signal transduction and stress response. However, little is known about the SBP-box genes in pepper (<i>CaSBP</i>), especially in the process of <i>Phytophthora capsici</i> infection. In this study, a novel gene (<i>CaSBP12</i>) was selected from the <i>CaSBP</i> gene family, which was isolated from the pepper genome database in our previous study. The <i>CaSBP12</i> gene was located in the nucleus of the cell and its silencing in the pepper plant enhanced the defense response against <i>Phytophthora capsici</i> infection. After inoculation with <i>Phytophthora capsici</i>, the root activity of the <i>CaSBP12</i>-silenced plants is compared to control plants, while malondialdehyde (MDA) content is compared viceversa. Additionally, the expression of defense related genes (<i>CaPO1</i>, <i>CaSAR8.2</i>, <i>CaBPR1,</i> and <i>CaDEF1</i>) in the silenced plants were induced to different degrees and the peak of <i>CaSAR8.2</i> and <i>CaBPR1</i> were higher than that of <i>CaDEF1.</i> The <i>CaSBP12</i> over-expressed <i>Nicotiana benthamiana</i> plants were more susceptible to <i>Phytophthora capsici</i> infection with higher EC (electrical conductivity) and MDA contents as compared to the wild-type. The relative expression of defense related genes (<i>NbDEF</i>, <i>NbNPR1</i>, <i>NbPR1a,</i> and <i>NbPR1b</i>) in transgenic and wild-type <i>Nicotiana benthamiana</i> plants were induced, especially the <i>NbPR1a</i> and <i>NbPR1b</i>. In conclusion, these results indicate that <i>CaSBP12</i> gene negative regulates the defense response against <i>Phytophthora capsici</i> infection which suggests their potentially significant role in plant defense. To our knowledge, this is the first report on <i>CaSBP</i> gene which negative regulate defense response.