Integrated Histological, Ultrastructural, and Transcriptomic Analyses Reveal New Insights into Stamen Development in Cytoplasmic Male Sterile Tobacco (CMS K326)

Cytoplasmic male sterility (CMS) is a crucial tool for exploiting plant heterosis, though its underlying mechanisms in tobacco remain incompletely understood. In this study, Tobacco CMSK326, derived from a naturally occurring variant of <i>Nicotiana tabacum</i>, exhibited a range of stamen abnormalities, including stamen degeneration, stamen absence, and carpelloid, petaloid, and sepaloid traits. Histological and electron microscopy showed that CMS K326 and its maintainer differentiated at the early bud stage. Analysis of differentially expressed genes (DEGs) revealed abnormal expressions of several key genes, including <i>WUSCHEL</i> (<i>WUS</i>), <i>GLOBOSA</i> (<i>GLO</i>), <i>SUPERMAN</i> (<i>SUP</i>), and auxin-related genes such as <i>AUX22</i>, during bud development. Weighted gene correlation network analysis (WGCNA) identified a module highly correlated with flower development, the tricarboxylic acid cycle (TCA), auxin, and the mitochondrial retrograde regulation signal molecules <i>CDKE1</i> and <i>KIN10</i>. The promoter regions of 19 out of the 42 hub genes in this module possess auxin cis-response elements. These results point to a correlation between auxin irregularities and stamen development in CMS K326.