Alternative splicing of the dormancy-associated MADS-box transcription factor gene PpDAM1 is associated with flower bud dormancy in 'Dangshansu' pear (Pyrus pyrifolia white pear group)

Alternative splicing (AS) plays a crucial role in plant growth, development and response to various environmental changes. However, whether alternative splicing of MADS-box transcription factors contributes to the flower bud dormancy process in fruit trees still remains unknown. In this work, the AS profile of genes in the dormant flower buds of 'Dangshansu' pear tree were examined. A total number of 3661 alternatively spliced genes were identified, and three mRNA isoforms of the dormancy associated MADS box (DAM) gene, PpDAM1, derived by alternative splicing, designated as PpDAM1.1, PpDAM1.2 and PpDAM1.3, were characterized. Bimolecular fluorescence complementation (BiFC) analysis indicated that AS of PpDAM1 didn't affect the nucleus localization and homo-/heterodimerization of PpDAM1.1, PpDAM1.2 and PpDAM1.3 proteins, but disturbed the translocation of PpDAM1.1/PpDAM1.1, PpDAM1.3/PpDAM1.3, PpDAM1.1/PpDAM1.3, and PpDAM1.2/PpDAM1.3 dimers to the nucleus. Constitutive expression of PpDAM1.2, but not PpDAM1.1 and PpDAM1.3, in Arabidopsis retarded the growth and development of transgenic plants. Further comparative expression analyses of PpDAM1.1, PpDAM1.2 and PpDAM1.3 in the flower buds of 'Dangshansu' and a less dormant pear cultivar, 'Cuiguan', exhibited that the expression of all the three isoforms in 'Dangshansu' were significantly higher than in 'Cuiguan', especially PpDAM1.2, which showed a predominantly higher expression than PpDAM1.1 and PpDAM1.3 in both cultivars. Our results suggest that alternative splicing of PpDAM1 could play a crucial role in pear flower bud dormancy process.