Abstract
The plant-specific LBD (LATERAL ORGAN BOUNDARIES domain) genes belong to a major family of transcription factor that encode a zinc finger-like domain. It has been shown that LBD genes play crucial roles in the growth and development of Arabidopsis and other plant species. However, no detailed information concerning this family is available for apple. In the present study, we analyzed the apple (Malus domestica) genome and identified 58 LBD genes. This gene family was tested for its phylogenetic relationships with homologous genes in the Arabidopsis genome, as well as its location in the genome, structure and expression. We also transformed one MdLBD gene into Arabidopsis to evaluate its function. Like Arabidopsis, apple LBD genes also have a conserved CX2CX6CX3C zinc finger-like domain in the N terminus and can be divided into two classes. The expression profile indicated that apple LBD genes exhibited a variety of expression patterns, suggesting that they have diverse functions. At the same time, the expression analysis implied that members of this apple gene family were responsive to hormones and stress and that they may participate in hormone-mediated plant organogenesis, which was demonstrated with the overexpression of the apple LBD gene MdLBD11, resulting in an abnormal phenotype. This phenotype included upward curling leaves, delayed flowering, downward-pointing flowers, siliques and other abnormal traits. Based on these data, we concluded that the MdLBD genes may play an important role in apple growth and development as in Arabidopsis and other species.
Highlights
LBD (LATERAL ORGAN BOUNDARIES domain) gene in Arabidopsis is a newly discovered and unique transcription factor family that has been assigned to this functional group on the basis of its nuclear localization and capacity to bind to a DNA motif [1,2,3,4,5]
Each of them was featured with a conserved LOB domain which ubiquitously exists in LBD genes of other plant species [4,6]
The cDNA of MdLBD11L was isolated with a RACE approach
Summary
LBD (LATERAL ORGAN BOUNDARIES domain) gene in Arabidopsis is a newly discovered and unique transcription factor family that has been assigned to this functional group on the basis of its nuclear localization and capacity to bind to a DNA motif [1,2,3,4,5]. LBD genes were found only in plant databases, indicating that this unique gene family may only regulate plant-specific processes [6]. The zinc-fingerlike domain is presumably required for DNA binding, and the Cterminal leucine zipper-like sequence is probably involved in protein dimerization [6,7] LBD proteins have varied expression patterns ranging from temporal to tissue differences, suggesting that they may function in diverse processes [6]. When observed under normal growth conditions, no obvious phenotype could be found in some loss-offunction lbd mutants, indicating that the LBD gene is functionally redundant or required during growth under specific environmental conditions [1,6,11]
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