The MADS-box gene CmAP1 promotes flowering and petal development in Chinese chestnut (Castanea mollissima)

Chinese chestnut (Castanea mollissima) is an economically and ecologically important woody nut crop. In C. mollissima, flowering is fundamental for nut yield. The MADS-box gene APETALA 1 (AP1) plays essential roles in floral initiation and floral organ development in many plants. However, the function of the AP1 gene CmAP1 in C. mollissima is still unclear. Here, we cloned the coding sequence (CDS) and promoter of CmAP1 and analyzed the function of this gene.

The CDS of CmAP1 is 741 bp and encodes a 246-amino acid protein. Subcellular analysis revealed that CmAP1 localizes to the nucleus. GUS driven by the CmAP1 promoter was expressed in seedlings and in leaf margins, petals, and carpels of transgenic Arabidopsis (Arabidopsis thaliana). RNA in situ hybridization indicated that CmAP1 was mainly expressed in the inflorescence meristem, floral primordia, sepal primordia, petal primordia, stamen primordia, and carpel primordia during the early stage of flower development. An auxin response element (TGA element), jasmonic acid response element (TGACG motif), and WRKY binding site (W-box element) were identified in the CmAP1 promoter. Heterologous expression of CmAP1 in wild-type and ap1-11 Arabidopsis resulted in early flowering. Notably, the expression of CmAP1 rescued the loss of the petal whorl in the ap1-11 mutant. AtAP1, AtSEP1, AtSEP2, AtSEP3, and AtSEP4 were upregulated in CmAP1-expressing Arabidopsis plants.

These findings suggest that CmAP1 promotes flowering and plays a key role in petal development. Our findings help reveal the regulatory mechanism of flowering and flower development in C. mollissima, providing a practical basis for increasing yield in Chinese chestnut.