Methyl Jasmonate (MeJA) Promotes the Self-Pollen Tube Growth of Camellia oleifera by Regulating Lignin Biosynthesis

Self-incompatibility (SI) poses a significant reproductive barrier, severely impacting the yield, quality, and economic value of <i>Camellia oleifera</i>. In this study, methyl jasmonate (MeJA) was employed as an exogenous stimulus to alleviate SI in <i>C. oleifera</i>. The research findings revealed that an exogenous dose of 1000 μmol·L^-1 MeJA enhanced the germination and tube growth of <i>C. oleifera</i> self-pollen and greatly improved ovule penetration (18.75%) and fertilization (15.81%), ultimately increasing fruit setting (18.67%). It was discovered by transcriptome analysis that the key genes (<i>CAD</i>, <i>C4H</i>) involved in the lignin production process exhibited elevated expression levels in self-pistils treated with MeJA. Further analysis showed that the lignin concentration in the MeJA-treated pistils was 31.70% higher compared with the control group. As verified by pollen germination assays in vitro, lignin in the appropriate concentration range could promote pollen tube growth. Gene expression network analysis indicated that transcription factor <i>bHLH</i> may be pivotal in regulating lignin biosynthesis in response to MeJA, which in turn affects pollen tubes. Further transient knockdown of <i>bHLH</i> (<i>Co_33962</i>) confirmed its important role in <i>C. oleifera</i> pollen tube growth. In summary, the application of MeJA resulted in the stimulation of self-pollen tube elongation and enhanced fruit setting in <i>C. oleifera</i>, which could be associated with the differential change in genes related to lignin synthesis and the increased lignin content.