Expression of the ASYMMETRIC LEAVES2 gene in the adaxial domain of Arabidopsis leaves represses cell proliferation in this domain and is critical for the development of properly expanded leaves.
ABSTRACT The ASYMMETRIC LEAVES2 (AS2) gene, a member of the AS2/LOB gene family, and the ASYMMETRIC LEAVES1 (AS1) gene of Arabidopsis thaliana participate in the development of a symmetrical, expanded lamina. We report here the patterns of expression of these genes, and the importance of the sites of such expression in leaf development. Transcripts of both genes accumulated in the entire leaf primordia at early stages, but the patterns of accumulation changed as the leaves expanded. AS2 and AS1 transcripts were detected, respectively, in the adaxial domain and in the inner domain between the adaxial and abaxial domains of leaves. The ratios of numbers of adaxial cells to abaxial cells in cotyledons of corresponding mutant lines were greater than the ratios in wild-type cotyledons. The low levels of ectopic expression of AS2 under the control of the AS1 promoter in as2 mutant plants restored an almost normal phenotype in some cases, but also resulted in flatter leaves than those of wild-type plants. Strong expression of the construct in wild-type and as2 plants, but not as1 plants, resulted in the formation of narrow, upwardly curled leaves. Our results indicate that AS2 represses cell proliferation in the adaxial domain in the presence of AS1, and that adaxial expression of AS2 at an appropriate level is critical for the development of a symmetrical, expanded lamina. Real-time RT-PCR analysis revealed that mutation of either AS2 or AS1 resulted in an increase in the levels of transcripts of ETTIN (ETT; also known as AUXIN RESPONSE FACTOR3, ARF3) and KANADI2 (KAN2), which are abaxial determinants, and YABBY5 (YAB5). Thus, AS2 and AS1 might negatively regulate the expression of these genes in the adaxial domain, which might be related to the development of flat and expanded leaves.
Article: FILAMENTOUS FLOWER controls lateral organ development by acting as both an activator and a repressor.[show abstract] [hide abstract]
ABSTRACT: BACKGROUND: The YABBY (YAB) family of transcription factors participate in a diverse range of processes that include leaf and floral patterning, organ growth, and the control of shoot apical meristem organisation and activity. How these disparate functions are regulated is not clear, but based on interactions with the LEUNIG-class of co-repressors, it has been proposed that YABs act as transcriptional repressors. In the light of recent work showing that DNA-binding proteins associated with the yeast co-repressor TUP1 can also function as activators, we have examined the transcriptional activity of the YABs. RESULTS: Of the four Arabidopsis YABs tested in yeast, only FILAMENTOUS FLOWER (FIL) activated reporter gene expression. Similar analysis with Antirrhinum YABs identified the FIL ortholog GRAMINIFOLIA as an activator. Plant-based transactivation assays not only confirmed the potential of FIL to activate transcription, but also extended this property to the FIL paralog YABBY3 (YAB3). Subsequent transcriptomic analysis of lines expressing a steroid-inducible FIL protein revealed groups of genes that responded either positively or negatively to YAB induction. Included in the positively regulated group of genes were the polarity regulators KANADI1 (KAN1), AUXIN RESPONSE FACTOR 4 (ARF4) and ASYMMETRIC LEAVES1 (AS1). We also show that modifying FIL to function as an obligate repressor causes strong yab loss-of-function phenotypes. CONCLUSIONS: Collectively these data show that FIL functions as a transcriptional activator in plants and that this activity is involved in leaf patterning. Interestingly, our study also supports the idea that FIL can act as a repressor, as transcriptomic analysis identified negatively regulated FIL-response genes. To reconcile these observations, we propose that YABs are bifunctional transcription factors that participate in both positive and negative regulation. These findings fit a model of leaf development in which adaxial/abaxial patterning is maintained by a regulatory network consisting of positive feedback loops.BMC Plant Biology 10/2012; 12(1):176. · 3.45 Impact Factor
Article: Meta-analyses of microarrays of Arabidopsis asymmetric leaves1 (as1), as2 and their modifying mutants reveal a critical role of the ETT pathway in stabilization of adaxial-abaxial patterning and cell division during leaf development.[show abstract] [hide abstract]
ABSTRACT: It is necessary to use algorithms to analyze gene expression data from DNA microarrays, such as in clustering and machine-learning. Previously, we developed the knowledge-based fuzzy adaptive resonance theory (KB-FuzzyART), a clustering algorithm suitable for analyzing gene expression data, to find clues for identifying gene networks. Leaf primordia form around the shoot apical meristem, which consists of indeterminate stem cells. Upon initiation of leaf development, adaxial-abaxial patterning is crucial for lateral expansion, via cellular proliferation, and the formation of flat symmetric leaves. Many regulatory genes that specify such patterning have been identified. Analysis by the KB-FuzzyART and subsequent molecular and genetic analyses previously showed that ASYMMETRIC LEAVES1 (AS1) and AS2 repress the expression of some abaxial-determinant genes, such as AUXIN RESPONSE FACTOR3 (ARF3)/ETTIN (ETT) and ARF4, which are responsible for defects in leaf adaxial-abaxial polarity in as1 and as2. In the present study, genetic analysis revealed that ARF3/ETT and ARF4 were regulated by modifier genes, BOBBER1 (BOB1) and ELONGATOR3 (ELO3) together with AS1-AS2. We analyzed expression arrays with as2 elo3 and as2 bob1 and extracted genes downstream of ARF3/ETT by using KB-FuzzyART and molecular analyses. The results showed that expression of Kip-related protein genes (KRPs) (for inhibitors of cyclin-dependent protein kinases) and Isopentenyltransferase gene (IPT) (for biosynthesis of cytokinin) were controlled by AS1-AS2 through ARF3/ETT and ARF4 functions, which suggests that the AS1-AS2-ETT pathway plays a critical role in controlling the cell division cycle and the biosynthesis of cytokinin around SAM to stabilize leaf development in Arabidopsis thaliana.Plant and Cell Physiology 02/2013; · 4.70 Impact Factor
Article: A Genome-Wide Analysis of the LBD (LATERAL ORGAN BOUNDARIES Domain) Gene Family in Malus domestica with a Functional Characterization of MdLBD11.[show abstract] [hide abstract]
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 and other plant species. However, no detailed information concerning this family is available for apple. In the present study, we analyzed the apple () genome and identified 58 genes. This gene family was tested for its phylogenetic relationships with homologous genes in the genome, as well as its location in the genome, structure and expression. We also transformed one gene into to evaluate its function. Like , apple genes also have a conserved CXCXCXC zinc finger-like domain in the N terminus and can be divided into two classes. The expression profile indicated that apple 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 gene , 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 genes may play an important role in apple growth and development as in and other species.PLoS ONE 01/2013; 8(2):e57044. · 4.09 Impact Factor