Transcript-Wide Identification and Characterization of the BBX Gene Family in Trichosanthes kirilowii and Its Potential Roles in Development and Abiotic Stress

<i>The B-box (BBX) protein</i> has an impact on flowering physiology, photomorphogenesis, shade effects, and responses to both biotic and abiotic stresses. Although recent research described the BBX gene family in numerous plants, knowledge of the BBX gene in <i>Trichosanthes kirilowii</i> was sparse. In this study, we identified a total of 25 <i>TkBBX</i> genes, and phylogenetic analysis showed that these genes were divided into five subfamilies. Analyses of gene structure and motifs for each group found relative conservation. Ka/Ks values showed that most <i>TkBBX</i> genes have undergone negative selection. qRT-PCR analyses revealed that <i>TkBBX1</i>, <i>TkBB4</i>, <i>TkBBX5</i>, <i>TkBBX7</i>, <i>TkBBX15</i>, <i>TkBBX16</i>, <i>TkBBX17</i>, <i>TkBBX19</i>, and <i>TkBBX21</i> genes respond to salt and drought treatment. Furthermore, we cloned <i>TkBBX7</i> and <i>TkBBX17</i> genes and performed a subcellular localization experiment, which revealed that these two genes were both located in the nucleus. Transgenic yeast experiments demonstrated that <i>TkBBX7</i> and <i>TkBBX17</i> enhanced yeast tolerance to both salt and drought stresses. These findings provide a theoretical foundation for further investigation on the functions of <i>TkBBX</i> genes in <i>Trichosanthes kirilowii</i>.