ASYMMETRIC LEAVES2 Gene Research Articles

Genome-wide analyses of LATERAL ORGAN BOUNDARIES in cassava reveal the role of LBD47 in defence against bacterial blight.

The Arabidopsis thaliana ASYMMETRIC LEAVES2 (AS2) gene is responsible for the development of flat, symmetric, and extended leaf laminae and their veins. The AS2 gene belongs to the plant-specific AS2-LIKE/LATERAL ORGAN BOUNDARIES (LOB)-domain (ASL/LBD), which consists of 42 proteins in Arabidopsis with a conserved amino-terminal domain known as the AS2/LOB domain, and a variable carboxyl-terminal region. AS2/LOB domain consists of an amino-terminal (N-terminal) that contains a cysteine repeat (the C-motif), a conserved glycine residue, and a leucine-zipper-like. AS2/LOB domain has been characterised in plants such as A. thaliana, Zea mays, and Oryza sativum. Nevertheless, it remains uncharacterised in cassava (Manihot esculenta). Characterisation and identification of cassava ASL/LBD genes using the computational algorithms, hidden Markov model profiles (PF03195), determined 55 ASL/LBD genes (MeASLBD1 to MeASLBD55). The gene structure and motif composition were conserved in MeASLBDs, while the expression profiles of these genes were highly diverse, implying that they are associated with diverse functions. Weighted gene co-expression network analysis (WGCNA) of target genes and promoter analysis suggest that these MeASLBDs may be involved in hormone and stress responses. Furthermore, the analysis of cis-regulatory elements in promoter regions suggested that MeASLBDs may be involved in the plant phytohormone signal response. The transcriptome data of cassava under biotic and abiotic stresses revealed that MeASLBD46 and MeASLBD47 greatly respond to disease and drought. The MeASLBD47 gene was selected for functional analysis. The result indicated that MeASLBD47 significantly mitigated the virulence of cassava bacterial blight (XamCHN11) through Real-Time Quantitative Reverse Transcription PCR (qRT-PCR) and Virus-induced gene silencing (VIGS). These findings provided a comprehensive analysis of ASL/LBD genes and laid the groundwork for future research to understand ASL/LBD genes.

SQUAMOSA PROMOTER BINDING PROTEIN-LIKE 2 controls floral organ development and plant fertility by activating ASYMMETRIC LEAVES 2 in Arabidopsis thaliana.

A network of genes is coordinately expressed to ensure proper development of floral organs and fruits, which are essential for generating new offspring in flowering plants. In Arabidopsis thaliana, microRNA156 (miR156) plays a role in regulating the development of flowers and siliques by targeting members of the SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) gene family. Despite the important roles of the miR156/SPL network, our understanding of its downstream genes that are involved in floral organ and silique growth is still incomplete. Here, we report that the miR156/SPL2 regulatory pathway regulates pollen production, fertility rate, and the elongation of floral organs, including petals, sepals, and siliques in Arabidopsis. Transgenic plants exhibiting both overexpression of miR156 and dominant-negative alleles of SPL2 had reduced ASYMMETRIC LEAVES 2 (AS2) transcript levels in their siliques. Furthermore, their fertility phenotype was similar to that of the AS2 loss-of-function mutant. We also demonstrate that the SPL2 protein binds to the 5'UTR of the AS2 gene in vivo, indicating that AS2 is directly regulated by SPL2. Our results suggest that the miR156/SPL2 pathway affects floral organs, silique development and plant fertility, as well as directly regulates AS2 expression.

ASYMMETRIC LEAVES2 gene, a member of LOB/AS2 family of Arabidopsis thaliana, causes an abaxializing leaves in transgenic cockscomb

The leaf primordium derives from the peripheral zone of shoot apical meristem. During the formation of leaf primordia, they need to establish the proximodistal, mediolateral, and ab/adaxial axes. Among these axes, the ab/adaxial axis might be the most important. ASYMMETRIC LEAVES2 (AS2) gene is a member of AS2/LATERAL ORGAN BOUNDARY (LOB) family of Arabidopsis thaliana. In this work, we transformed 35S:AS2 transgene constructs to cockscomb (Celosia cristata) via Agrobacterium tumefaciens. All primary transformants subsequently obtained were placed into phenotypic categories and self-pollinated. As a whole, a total of 44 T1 35S:AS2 cockscomb plants obtained were grouped into two major categories: (I) slightly wrinkled leaves (28/44), (II) extremely curved leaves (16/44), on the basis of their leaf phenotypes. Furthermore, we characterized the anatomical features of these malformed leaves; and found the transformation of adaxial cell types into abaxial cell ones. A series of data suggest that AS2 might be involved in the determination of abaxial polarity in cockscomb plants. However, a few research teams have reported that AS2 might be involved in the determination of adaxial polarity in leaf primodia of Arabidopsis thaliana. These data above indicate that the roles of the same ab/adaxial determinant might differ between distinct species. At last, the different function of AS2 in distinct species was discussed.

Molecular genetic studies on ASYMMETRIC LEAVES2 (AS2) of Arabidopsis: Insight into the function of the AS2 protein

The ASYMMETRIC LEAVES2 (AS2) gene is involved in leaf development along adaxial-abaxial, medial-lateral and proximal-distal axes in Arabidopsis. The AS2 gene belongs to the AS2/LATERAL ORGAN BOUNDARIES (LOB) family. There are 42 members of the AS2/LOB family in the Arabidopsis genome. Many recent studies revealed that AS2/LOB family genes are involved in various physiological processes including the regulation of development and metabolism in plants. The approximately 100 amino acid AS2/LOB-domain, which defines this family, is highly conserved. Conserved regions include the C-motif, an internal region containing an invariant glycine residue, and a leucine-zipper-like motif, in the case of class I proteins. The conserved AS2/LOB-domain of AS2 cannot be functionally replaced by those of other members of the family. AS2 acts in a same pathway as that of AS1, which is an ortholog of ROUGH SHEATH2 of maize and PHANTASTICA of snapdragon. Recent molecular genetic studies for the role of AS2 provided important information. The regulation of gene expression and leaf development by AS2 is genetically linked with the regulations based on chromatin level, post-transcriptional level, protein metabolism and cell proliferation. These novel insights contribute to a better understanding of the role of AS2/LOB family genes for plant morphogenesis and physiological responses.

Rice OsAS2 Gene, a Member of LOB Domain Family, Functions in the Regulation of Shoot Differentiation and Leaf Development

LATERALORGAN BOUNDARIES DOMAIN (LBD) genes, a novel plant-specific family, play specific roles in plant development. Although function of ASYMMETRIC LEAVES2 (AS2), a LBD gene, was extensively studied in Arabidopsis of dicots, little is known on the role of its ortholog in rice of monocots. In this study, a LBD gene that shares higher homology with Arabidopsis AS2 gene was identified in rice and it was designated as OsAS2. Its transcripts were detected throughout predicted leaf primordia in shoot apical meristem (SAM), leaf primordia, and young leaves. Overexpression of the OsAS2 gene inhibited shoot differentiation, promoted cell division, and delayed cell differentiation in rice calli. Transgenic plants with OsAS2 gene showed the aberrant twisted leaves, which lack auricle, and leaf structure was abnormal. Furthermore, a few genes involved in shoot meristem development were upregulated in transgenic plants. Our results suggest that proper expression of the OsAS2 gene is required for shoot differentiation and leaf development in rice.

Function of the ASYMMETRIC LEAVES1 and ASYMMETRIC LEAVES2 genes in leaf development of Arabidopsis

Summary: The ASYMMETRIC LEAVES1(AS1)and ASYMMETRIC LEAVES2(AS2)genes of Arabidopsis thaliana are involved in the establishment of the leaf venation system, which includes the prominent midvein; as well as in the development of a symmetric flat lamina. Both AS1 and AS2 genes are involved in repression of class1 knox homeobox genes in leaves. We have characterized the AS2 gene, which appears to encode a novel protein with cysteine repeats(Cmotif), a conserved glycine residue, and a leucine-zipper-like sequence in the amino-terminal half of the primary sequence. The AS2 protein belongs to a novel family of proteins that we have designated the AS2 family. Overexpression of AS2 cDNA in transgenic Arabidopsis plants resulted in upwardly curled leaves, which differed markedly from the downwardly curled leaves generated by loss-of-function mutation of AS2. Our results further suggest that AS2 functions to regulate the formation of a flat leaf lamina in the presence of the AS1 gene.

The ASYMMETRIC LEAVES2 gene of Arabidopsis thaliana, required for formation of a symmetric flat leaf lamina, encodes a member of a novel family of proteins characterized by cysteine repeats and a leucine zipper.

The ASYMMETRIC LEAVES2 (AS2) gene of Arabidopsis thaliana is involved in the establishment of the leaf venation system, which includes the prominent midvein, as well as in the development of a symmetric lamina. The gene product also represses the expression of class 1 knox homeobox genes in leaves. We have characterized the AS2 gene, which appears to encode a novel protein with cysteine repeats (designated the C-motif) and a leucine-zipper-like sequence in the amino-terminal half of the primary sequence. The Arabidopsis genome contains 42 putative genes that potentially encode proteins with conserved amino acid sequences that include the C-motif and the leucine-zipper-like sequence in the amino-terminal half. Thus, the AS2 protein belongs to a novel family of proteins that we have designated the AS2 family. Members of this family except AS2 also have been designated ASLs (AS2-like proteins). Transcripts of AS2 were detected mainly in adaxial domains of cotyledonary primordia. Green fluorescent protein-fused AS2 was concentrated in plant cell nuclei. Overexpression of AS2 cDNA in transgenic Arabidopsis plants resulted in upwardly curled leaves, which differed markedly from the downwardly curled leaves generated by loss-of-function mutation of AS2. Our results suggest that AS2 functions in the transcription of a certain gene(s) in plant nuclei and thereby controls the formation of a symmetric flat leaf lamina and the establishment of a prominent midvein and other patterns of venation.