Transcriptome analysis provides new insights into leaf shape variation in birch

KEY MESSAGE: The present study revealed many functional molecules for leaf splitting during the apical bud development and the switch development from the apical buds to leaf marginal tissues. The lobe, an important character of leaf architecture, is present in Betula pendula ‘Dalecarlica’. The presence of split lobes is of great significance in plant growth and development. The molecular mechanisms underlying leaf shape variation remains poorly understood in birch. Herein, the plants of B. pendula and B. pendula ‘Dalecarlica’ were designated as O (original variety) and V (variety), respectively. We performed transcriptome sequencing on the plant materials of apical buds from O (OSAM), apical buds from V (VSAM), leaf sinus from O (OS), leaf margin from O (OM), leaf sinus from V (VS) and lobe from V (VL) to uncover the candidate genes for sculpturing leaf margin. Analysis of the differential transcripts revealed 37 genes between OSAM and VSAM, 3702 genes between VSAM and VS, 3624 genes between VSAM and VL, 1731 genes between OSAM and OS, 1678 genes between OSAM and OM, 9 genes between VS and VL, 67 genes between OS and VS, and 45 genes between OM and VL. Functional analysis of genes showed that many genes related to auxin synthesis, cell division and antioxidant defense were detected at the apical bud stage. Some genes involved in transcription factors, cell proliferation, and auxin synthesis and signaling response were recorded during the switch development from the apical buds to leaf marginal tissues. Moreover, one to three genes coding for glycine-rich proteins (GRPs) were observed in each comparative combination. Particularly, GRP homology was weakly expressed in VS and strongly expressed in VL. Overall, these discovered genes, especially GRPs, might contribute to the development of lobed leaves. Our study provides useful information for leaf shape modification of woody plants.