Chimeric genes contribute to the evolution of diverse functions in plants and animals. However, new chimeric genes also increase the risk of developmental defects. Here, we show that the chimeric gene ( ) is responsible for genic male sterility in the widely used canola line 7365A ( ). originated via exon shuffling ∼4.6 million years ago. It causes defects in the normal functions of plastids and induces aborted anther formation and/or albino leaves and buds. Evidence of the age of the mutation, its tissue expression pattern, and its sublocalization indicated that it coevolved with (). In , results in complete male sterility that can be rescued by , suggesting that might restore fertility through effects on protein level. Another suppressor gene, , rescues sterility by reducing the level of transcription of Our results suggest that plants have coevolved altered transcription patterns and neofunctionalization of duplicated genes that can block developmental defects resulting from detrimental chimeric genes.

Brassinosteroids (BRs) are plant-specific steroidal hormones; BR homeostasis is crucial for various aspects of plant growth and development. However, to date, the BR inactivation process has not been thoroughly elucidated. In this study, we identified and characterized a novel BAHD family acyltransferase gene, BRASSINOSTEROID INACTIVATOR2 (BIA2), involved in BR inactivation. BIA2-overexpressing (OE-BIA2) plants displayed typical BR-deficient phenotypes, which were rescued by exogenous BR treatment. Real-time qRT-PCR and transcriptome analyses showed that expression levels of virtually all of the BR biosynthetic genes were increased, whereas the expression of many BR inactivation genes was reduced in OE-BIA2 plants. Root inhibition assays showed that the root growth of OE-BIA2 plants was inhibited. We obtained plants with an intermediate phenotype by crossing the OE-BIA2 plants with BRASSINOSTEROID-INSENSITIVE1 (BRI1)-overexpressing plants. The null BIA2 mutants had longer hypocotyls in the dark. BIA2 was predominantly expressed in roots, and its expression was induced by 24-epibrassinolide or dark treatment, but it exhibited a differential expression pattern compared with its homologue, BIA1. Furthermore, genetic transformation with point-mutant and deleted-BIA2 constructs confirmed that the HXXXD motif is essential for the function of BIA2. Taken together, these findings indicate that BIA2 is a typical BAHD acyltransferase that is involved in BR homeostasis and may inactivate bioactive BRs by esterification, particularly in roots and hypocotyls under dark conditions.

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