Key genes BpMYB80 and BpMYB59 play important roles in regulating floral development in birch male flower mutants

The MYB family is one of the largest transcription factor families in eukaryotes. Members of the MYB family play various roles in regulating plant growth, development, and stress responses. However, research on key MYB genes and their functions during floral development in birch (Betula platyphylla) is extremely limited. This study investigated the anatomical structure of abnormal male flower development in a natural birch mutant and identified key genes using transcriptomics. The functions of these genes in regulating flowering time were further analyzed through heterologous transformation in Arabidopsis thaliana. The results showed that the abnormal development of the birch male flower mutant occurred during the tetrad stage, where the tapetum cells failed to undergo normal programmed cell death (PCD), leading to the failure of tetrad degradation and affecting the release of microspores and subsequent pollen wall formation, ultimately resulting in the male flower mutant. Transcriptomic data from different stages of the mutant identified BpMYB80 and BpMYB59 as potential key genes affecting birch floral development. Subcellular localization and transcriptional activation experiments revealed that BpMYB80 is specifically expressed in the nucleus, while BpMYB59 is localized in both the cell membrane and nucleus, with transcriptional activation activity. Heterologous genetic transformation in A. thaliana showed phenotypic differences in plant height and flowering time. The average height of Col-0 and BpMYB80-OE plants was about 20 cm, while BpMYB59-OE plants were significantly shorter, averaging 5-10 cm. Col-0 began bolting at the 5th week, while BpMYB59-OE started bolting at the 4th week, followed by a slow reproductive growth phase. BpMYB80-OE began bolting at the 3rd week, significantly earlier than other genotypes. Further studies showed that BpMYB80 and BpMYB59 differentially respond to gibberellin (GA). In BpMYB80-transgenic A. thaliana, the expression of GA biosynthesis genes AtGA3ox1 and AtGA3ox2, as well as flowering-related genes AtSOC1, AtLFY and AtFT, was significantly upregulated, while the expression of the DELLA protein family member AtRGA was downregulated. In contrast, in BpMYB59-transgenic A.thaliana, the expression of AtGA3ox1, AtGA3ox2, AtSOC1, AtLFY and AtFT was significantly downregulated, while AtRGA was upregulated. In conclusion, the key gene BpMYB80 in the birch male flower mutant may promote early flowering through the GA pathway, while BpMYB59 delays flowering time.