Integrating Genetic Mapping and BSR-Seq Analysis to Identify Candidate Genes Controlling Fruitfulness in Camellia sinensis

As nutrient allocation trade-offs occur between reproductive and vegetative development in crops, optimizing their partitioning holds promise for improving agricultural productivity and quality. Herein, we characterize the phenotypic diversity of the fruitfulness trait and identify associated genes in tea plants (<i>Camellia sinensis</i>). Over three consecutive years, we monitored the fruitfulness of an F₁ hybrid population (<i>n</i> = 206) derived from crosses of 'Emei Wenchun' and 'Chuanmu 217'. A marked variation was observed in the yield of individual plants, ranging from complete sterility (zero fruits) to exceptionally high fertility (1612 fruits). Using the high-resolution genetic linkage map and the fruitfulness data, we identified a stable major QTL designated as <i>qFN5</i>. To fine-map the underlying gene(s), artificial pollination experiments were conducted with extreme phenotype individuals (with the highest vs. lowest fruit numbers). Bulked segregant RNA sequencing (BSR-Seq) with ovules collected at two and seven days post-pollination (DPP) identified the genomic intervals that exhibit a high degree of overlap with <i>qFN5</i>. Analysis of expression dynamics combined with functional genomics data revealed a prominent candidate gene, <i>CsETR2</i> (TGY048509), which encodes an ethylene receptor protein. When <i>CsETR2</i> was overexpressed in <i>Arabidopsis thaliana</i>, the transgenic lines exhibited significantly decreased reproductive performance relative to the wild-type plants. Relative to the wild type, the transgenic lines exhibited a significant decline in several key traits: the number of effective panicles decreased by 72.5%, the seed setting rate dropped by 67.7%, and the silique length shortened by 38%. These findings demonstrate its role in regulating plant fruitfulness. Furthermore, yeast one-hybrid and dual-luciferase assays verified that <i>CsMYB15</i> (TGY110225) directly binds to the <i>CsETR2</i> promoter, thus repressing its transcription. In summary, our findings expand the understanding of genetic regulation underlying fruitfulness in tea plants and provide candidate target loci for breeding.