Genome-Wide Analysis of the Serine Carboxypeptidase-like (SCPL) Protein Family of Bitter Gourd and Functional Validation of McSCPL22 in Fusarium oxysporum f. sp. Momordicae (FOM) Resistance

Bitter gourd is increasingly being recognized for its value as a vegetable and medicinal use, but the molecular mechanisms of pathogen resistance remain relatively poorly understood. The serine carboxypeptidase-like (SCPL) protein family plays a key role in plant growth, pathogen defense, and so on. However, a comprehensive identification and functional characterization of the <i>SCPL</i> gene family has yet to be conducted in bitter melon. In this study, 32 <i>SCPL</i> genes were identified in bitter gourd and divided into three classes. The number of <i>SCPL</i> genes contained in the three clusters was 7, 7, and 18, respectively. Most <i>SCPL</i> gene promoters contain <i>cis</i>-acting elements with light, hormone, and stress responses. The RNA sequencing data showed that the expression of several <i>SCPL</i> genes changed significantly after pathogen infection. In particular, expression of the <i>McSCPL4</i>, <i>10</i>, <i>17</i>, <i>22</i>, and <i>25</i> genes increased substantially in the resistant varieties after infection, and their expression levels were higher than those in the susceptible varieties. These results suggested that genes such as <i>McSCPL4</i>, <i>10</i>, <i>17</i>, <i>22</i>, and <i>25</i> may play a significant role in conferring resistance to fungal infections. Moreover, the expression levels of the <i>McSCPL10</i>, <i>17</i>, <i>22</i>, <i>23,</i> and <i>25</i> genes were likewise significantly changed after being induced by salicylic acid (SA) and jasmonic acid (JA). In situ hybridization showed that <i>McSCPL22</i> was expressed in the vascular tissues of infected plants, which largely overlapped with the location of <i>Fusarium oxysporum</i> f. sp. <i>Momordicae</i> (FOM) infection and the site of hydrogen peroxide production. Our results showed that <i>McSCPL22</i> may be involved in the regulation of the SA and JA pathways and enhance resistance to FOM in bitter gourd plants. This is the first study to perform <i>SCPL</i> gene family analysis in bitter gourd. <i>McSCPL22</i> may have the potential to enhance FOM resistance in bitter gourd, and further investigation into its function is warranted. The results of this study may enhance the yield and molecular breeding of bitter gourd.