Abaxial Cells Research Articles

Phytochrome B interacts with LIGULELESS1 to control plant architecture and density tolerance in maize

Over the past few decades, significant improvements in maize yield have been largely attributed to increased plant density of upright hybrid varieties rather than increased yield per plant. However, dense planting triggers shade avoidance responses (SARs) that optimize light absorption but impair plant vigor and performance, limiting yield improvement through increasing plant density. In this study, we demonstrated that high-density-induced leaf angle narrowing and stem/stalk elongation are largely dependent on phytochrome B (phyB1/B2), the primary photoreceptor responsible for perceiving red (R) and far-red (FR) light in maize. We found that maize phyB physically interacts with the LIGULELESS1 (LG1), a classical key regulator of leaf angle, to coordinately regulate plant architecture and density tolerance. The abundance of LG1 is significantly increased by phyB under high R:FR light (low density) but rapidly decreases under low R:FR light (high density), correlating with variations in leaf angle and plant height under various densities. In addition, we identified the homeobox transcription factor HB53 as a target co-repressed by both phyB and LG1 but rapidly induced by canopy shade. Genetic and cellular analyses showed that HB53 regulates plant architecture by controlling the elongation and division of ligular adaxial and abaxial cells. Taken together, these findings uncover the phyB-LG1-HB53 regulatory module as a key molecular mechanism governing plant architecture and density tolerance, providing potential genetic targets for breeding maize hybrid varieties suitable for high-density planting.

BcBZR1 Regulates Leaf Inclination Angle in Non-Heading Chinese Cabbage (Brassica campestris ssp. chinensis Makino)

Brassinosteroids (BRs) play critical roles in plant growth by promoting cell elongation and division, leading to increased leaf inclination angles. BRASSINAZOLE RESISTANT 1 (BZR1) and BRI1-EMS-SUPPRESSOR 1 (BES1) act as transcription factors in the brassinosteroid signaling pathway and are involved in several physiological activities regulated by BRs. In this study, we identified and cloned BcBZR1 from the heitacai non-heading Chinese cabbage (NHCC) cultivar. The sequence analysis showed that the coding sequence length of BcBZR1 is 996 bp, encoding 331 amino acid residues. Subcellular localization assays showed that BcBZR1 is localized in the nucleus and cytoplasm and that BcBZR1 protein is transported to the nucleus after receiving BR signals. Compared with Col-0, the leaf inclination angle was smaller in BcBZR1-OX. The EBR treatment experiment indicated that BRs regulate the differential expression of paclobutrazol resistance1 (PRE1) and ILI1 binding bHLH1 (IBH1) in the adaxial and abaxial cells of the petiole through BZR1, thus regulating the leaf inclination angle. The bimolecular fluorescence complementation (BiFC) assay indicated that BcBZR1 interacts with C-repeat Binding Factor2 (BcCBF2) and CBF3. Taken together, our findings not only validate the function of BcBZR1 in leaf inclination angle distribution in non-heading Chinese cabbage, but also contribute to the mechanism of leaf inclination angle regulation in this species under cold stress.

Seasonal variation of stomatal characteristics of Ficus species grown in Zaria, North Western Nigeria

Foliar stomatal characteristics are among the commonly used characters for the identificationand delimitation of taxa. This study was carried out to determine variations in stomatalcharacteristics of some members in the Genus Ficus grown in Zaria, part of the Sudan Savanna zone of Nigeria. Eight different Ficus species grown in Zaria were used for the study. Microscopic observations of foliar stomatal characteristics were carried out following standard established protocols during both the dry and rainy seasons. Stomatal preparations were obtained using matured leaves by treating each leaf with sodium hypochlorite to clear the chlorophyll contents. Measurements of stomatal characters were made with the aid of an ocular micrometer and stage micrometer. Photomicrographs were taken. The data obtainedwere subjected to analysis of variance (ANOVA) with Duncan’s New Multiple Range Test used to separate significant means at 5 % level. The result obtained revealed significant difference (P≤0.05) in the stomatal characteristics of the Ficus species with season. Anomocytic stomata was detected in all the species. There were variations with abaxial stomata cell length ranging from 23.32-50.24 μm in dry season and in the rainy season, the abaxial cell length ranged between 26.78-46.43 μm. Also, the stomatal index in the dry season ranged from 1.30% to 27.16% while in the rainy season, it ranged from 15.29 % to 23.19 %.

PheLBD29, an LBD transcription factor from Moso bamboo, causes leaf curvature and enhances tolerance to drought stress in transgenic Arabidopsis

The lateral organ boundaries domain (LBD), a unique family of transcription factors in higher plants, plays a key role in plant growth and development, and stress response. Here, we report on the novel lateral organ boundaries domain (LBD) gene PheLBD29, a nuclear localization protein that can bind the conserved GCCCCG sequence, as determined by electrophoretic mobility shift assay (EMSA). PheLBD29 was highly expressed in blade leaf and significantly induced by polyethylene glycol (PEG). Overexpression of PheLBD29 leads to small and abaxially rolled leaves in Arabidopsis, and anatomically, 35S:PheLBD29 Arabidopsis leaves showed transformation of adaxial cells into abaxial cells. Moreover, overexpression of PheLBD29 in Arabidopsis increased plant tolerance to drought stress, by accumulation of more soluble sugars, less malondialdehyde (MDA), and had lower REL levels under drought stress. Transient expression assay revealed PheLBD29 directly bound to the promoter region of RAB18. In addition, 35S:PheLBD29 Arabidopsis showed higher sensitivity to abscisic acid (ABA) than the wild type. Therefore, we conclude that PheLBD29 may participate in the ABA-dependent signaling pathway to improve drought tolerance. Our study provides new evidence for a Moso bamboo LBD protein regulatory module in leaf curvature and drought resistance.

DWARF AND ROBUST PLANT regulates plant height via modulating gibberellin biosynthesis in chrysanthemum.

YABBY (YAB) genes are specifically expressed in abaxial cells of lateral organs and determine abaxial cell fate. However, most studies have focused on few model plants, and the molecular mechanisms of YAB genes are not well understood. Here, we identified a YAB transcription factor in chrysanthemum (Chrysanthemum morifolium), Dwarf and Robust Plant (CmDRP), that belongs to a distinct FILAMENTOUS FLOWER (FlL)/YAB3 sub-clade lost in Brassicaceae. CmDRP was expressed in various tissues but did not show any polar distribution in chrysanthemum. Overexpression of CmDRP resulted in a semi-dwarf phenotype with a significantly decreased active GA3 content, while reduced expression generated the opposite phenotype. Furthermore, plant height of transgenic plants was partially rescued through the exogenous application of GA3 and Paclobutrazol, and expression of the GA biosynthesis gene CmGA3ox1 was significantly altered in transgenic plants. Yeast one-hybrid, luciferase, and chromatin immunoprecipitation-qPCR analyses showed that CmDRP could directly bind to the CmGA3ox1 promoter and suppress its expression. Our research reveals a nonpolar expression pattern of a YAB family gene in dicots and demonstrates it regulates plant height through the GA pathway, which will deepen the understanding of the genetic and molecular mechanisms of YAB genes.

Specification of leaf dorsiventrality via a prepatterned binary readout of a uniform auxin input.

Developmental boundaries play an important role in coordinating the growth and patterning of lateral organs. In plants, specification of dorsiventrality is critical to leaf morphogenesis. Despite its central importance, the mechanism by which leaf primordia acquire adaxial versus abaxial cell fates to establish dorsiventrality remains a topic of much debate. Here, by combining time-lapse confocal imaging, cell lineage tracing and molecular genetic analyses, we demonstrate that a stable boundary between adaxial and abaxial cell fates is specified several plastochrons before primordium emergence when high auxin levels accumulate on a meristem prepattern formed by the AS2 and KAN1 transcription factors. This occurrence triggers a transient induction of ARF3 and an auxin transcriptional response in AS2-marked progenitors that distinguishes adaxial from abaxial identity. As the primordium emerges, dynamic shifts in auxin distribution and auxin-related gene expression gradually resolve this initial polarity into the stable regulatory network known to maintain adaxial-abaxial polarity within the developing organ. Our data show that spatial information from an AS2-KAN1 meristem prepattern governs the conversion of a uniform auxin input into an ARF-dependent binary auxin response output to specify adaxial-abaxial polarity. Auxin thus serves as a single morphogenic signal that orchestrates distinct, spatially separated responses to coordinate the positioning and emergence of a new organ with its patterning.

Integration of Core Mechanisms Underlying Plant Aerial Architecture.

Over the last decade or so important progress has been made in identifying and understanding a set of patterning mechanisms that have the potential to explain many aspects of plant morphology. These include the feedback loop between mechanical stresses and interphase microtubules, the regulation of plant cell polarity and the role of adaxial and abaxial cell type boundaries. What is perhaps most intriguing is how these mechanisms integrate in a combinatorial manner that provides a means to generate a large variety of commonly seen plant morphologies. Here, I review our current understanding of these mechanisms and discuss the links between them.

Overexpression of the MADS-box gene SIMBP21 alters leaf morphology and affects reproductive development in tomato

Fruit yield is the most important horticultural trait of tomato. SlMBP21, a SEPALLATA subclass MADS-box gene has been reported to have functions in regulating pedicel abscission zone identity and development and controlling sepal size in tomato. However, we generated transgenic tomato plants which overexpress SlMBP21 and found the transformants displayed curly leaves, abnormally shaped flowers with twisted and opened stamens, reduced yield parameters, and small and light seeds. Our studies on the gain-of-function phenotype and gene expression level showed that its novel aspects played important roles in determining leaf morphology, flower and inflorescence architecture, and seed size, as well as the fruit yield. Overexpression of SlMBP21 in tomato resulted in curly leaves with fewer leaflets due to the regulation of the critical leaf polarity genes that cause an imbalance between the midvein adaxial–abaxial cell growth. Defects in the architecture of flowers and inflorescences resulted in reduced fruit set. Furthermore, we demonstrated that SlMBP21 plays its role through inhibiting the expression of the genes involved in the determination of seed development in tomato and SlMBP21 protein can interact with other MADS-box protein (SlAGL11, TAGL1 and SlMBP3) to control seed size. Thus, these results suggest that overexpression of SlMBP21 causes multiple types of damage to plant growth and development, especially fruit yield, in tomato.

Mutation of SlARC6 leads to tissue-specific defects in chloroplast development in tomato

The proliferation and development of chloroplasts are important for maintaining the normal chloroplast population in plant tissues. Most studies have focused on chloroplast maintenance in leaves. In this study, we identified a spontaneous mutation in a tomato mutant named suffulta (su), in which the stems appeared albinic while the leaves remained normal. Map-based cloning showed that Su encodes a DnaJ heat shock protein that is a homolog of the Arabidopsis gene AtARC6, which is involved in chloroplast division. Knockdown and knockout of SlARC6 in wild-type tomato inhibit chloroplast division, indicating the conserved function of SlARC6. In su mutants, most mesophyll cells contain only one or two giant chloroplasts, while no chloroplasts are visible in 60% of stem cells, resulting in the albinic phenotype. Compared with mature tissues, the meristem of su mutants suggested that chloroplasts could partially divide in meristematic cells, suggesting the existence of an alternative mechanism in those dividing cells. Interestingly, the adaxial petiole cells of su mutants contain more chloroplasts than the abaxial cells. In addition, prolonged lighting can partially rescue the albinic phenotypes in su mutants, implying that light may promote SlACR6-independent chloroplast development. Our results verify the role of SlACR6 in chloroplast division in tomato and uncover the tissue-specific regulation of chloroplast development.

Relationship between salicylic acid and resistance to mite in strawberry

Abstract The two-spotted spider mite (TSSM) Tetranychus urticae is a polyphagous pest which infests several wild and cultivated species of plants worldwide. To date, this mite is the most deleterious pest attacking the strawberry plant under a protected environment. Exogenously applied salicylic acid (SA) has been found to induce resistance to biotic and abiotic stresses. Morpho-anatomical changes in strawberry leaflets and TSSM preference tests were investigated in response to SA treatment. Plants grown in a greenhouse were foliar sprayed with different concentrations of SA (0 mg · L−1, 25 mg · L−1, 50 mg · L−1, 75 mg · L−1 and 100 mg · L−1). After the third application, certain parameters including the number of glandular and non-glandular trichomes, thickness of leaflet, abaxial cell wall, adaxial cell wall, palisade and lacunous parenchyma and mesophyll were measured using scanning electronic microscopy (SEM). Two-choice and non-choice assays were employed to verify the TSSM preference. Exogenous treatment with SA promoted morpho-anatomical changes in the following parameters, namely: thickness of the leaflets, mesophyll, lacunous and palisade parenchyma, cell wall (abaxial and adaxial) and the number of glandular and non-glandular trichomes in strawberry leaflets. In general, TSSM preferred less leaflets treated with SA compared with the control in a two-choice assay. A lesser number of TSSM eggs and live females were also recorded in leaflets treated with SA compared with the control plants in no-choice assays. The values of the number of eggs and live females correlated negatively with those obtained for the morpho-anatomical traits induced by exogenous SA.

Patterning a Leaf by Establishing Polarities.

Leaves are the major organ for photosynthesis in most land plants, and leaf structure is optimized for the maximum capture of sunlight and gas exchange. Three polarity axes, the adaxial–abaxial axis, the proximal-distal axis, and the medial-lateral axis are established during leaf development to give rise to a flattened lamina with a large area for photosynthesis and blades that are extended on petioles for maximum sunlight. Adaxial cells are elongated, tightly packed cells with many chloroplasts, and their fate is specified by HD-ZIP III and related factors. Abaxial cells are rounder and loosely packed cells and their fate is established and maintained by YABBY family and KANADI family proteins. The activities of adaxial and abaxial regulators are coordinated by ASYMMETRIC LEAVES2 and auxin. Establishment of the proximodistal axis involves the BTB/POZ domain proteins BLADE-ON-PETIOLE1 and 2, whereas homeobox genes PRESSED FLOWER and WUSCHEL-RELATED HOMEOBOX1 mediate leaf development along the mediolateral axis. This review summarizes recent advances in leaf polarity establishment with a focus on the regulatory networks involved.

Deep Imaging Analysis in VISUAL Reveals the Role of YABBY Genes in Vascular Stem Cell Fate Determination

Stem cells undergo cell division and differentiation to ensure organized tissue development. Because plant cells are immobile, plant stem cells ought to decide their cell fate prior to differentiation, to locate specialized cells in the correct position. In this study, based on a chemical screen, we isolated a novel secondary cell wall indicator BF-170, which binds to lignin and can be used to image in vitro and in situ xylem development. Use of BF-170 to observe the vascular differentiation pattern in the in vitro vascular cell induction system, VISUAL, revealed that adaxial mesophyll cells of cotyledons predominantly generate ectopic xylem cells. Moreover, phloem cells are abundantly produced on the abaxial layer, suggesting the involvement of leaf adaxial-abaxial polarity in determining vascular cell fate. Analysis of abaxial polarity mutants highlighted the role of YAB3, an abaxial cell fate regulator, in suppressing xylem and promoting phloem differentiation on the abaxial domains in VISUAL. Furthermore, YABBY family genes affected in vivo vascular development during the secondary growth. Our results denoted the possibility that such mediators of spatial information contribute to correctly determine the cell fate of vascular stem cells, to conserve the vascular pattern of land plants.

Semi-dwarf 1 (sd1) gene enhances light penetration into the canopy through regulating leaf inclination angle in rice

Manipulating leaf inclination angle is a feasible approach to improve canopy photosynthesis and dry matter production in rice (Oryza sativa) via enhancing light penetration into the canopy. The importance of the semi-dwarf 1 (sd1) gene, a loss-of-function allele of SD1 encoding GA-20 oxidase-2 in gibberellin (GA) biosynthesis, in rice yield through improving lodging resistance is well known. However, little is known about the effects of sd1 as well as GA on leaf inclination angle. A near-isogenic line carrying the ‘Takanari’ sd1 allele in the ‘Koshihikari’ genetic background (NIL-sd1) had leaves with larger (more erect) leaf inclination angle and showed a smaller canopy extinction coefficient at the ripening stage than did ‘Koshihikari’. Furthermore, the leaf inclination angle of ‘Reimei’, an sd1 mutant in the ‘Fujiminori’ background, and of several other sd1 mutants in ‘Koshihikari’ background, was larger at the ripening stage than in parental lines, ‘Fujiminori’ and ‘Koshihikari’, respectively. The flag leaves of ‘Koshihikari’ plants treated with a GA biosynthesis inhibitor, paclobutrazol (PBZ), displayed a larger leaf inclination angle than did those of mock-treated plants during ripening. Treatment at the lamina joint of a flag leaf with exogenous GA3 or brassinolide (BL) significantly decreased leaf inclination angle. BL treatment increased the thickness of lamina joint tissue and the longitudinal cell length on the adaxial side of the marginal region of lamina joint, whereas GA3 treatment only increased the longitudinal cell length. NIL-sd1 had a lamina joint with decreased longitudinal adaxial cell length, but no difference in abaxial cell length nor tissue thickness in lamina joint cross section compared with that of ‘Koshihikari’. Thus, sd1 regulates the leaf inclination angle via a GA-based mechanism but not via BL involved in the crosstalk with GA.

Cryptic speciation in the herbaceous bamboo genus Piresia (Poaceae, Olyreae)

AbstractPiresia, a small genus of herbaceous bamboos, has a geographical disjunction between the Caribbean and northern/western South America and the north-eastern Atlantic Forest in Brazil. Piresia leptophylla is reported from western Amazonia (WA) and the north-eastern Atlantic Forest (NAF), but its occurrence in western Amazonia is questionable. Using an integrative approach, we combined traditional morphological analysis, anatomy and niche modelling. The results revealed few macromorphological differences between WA and NAF specimens (only plant height, leaf length, lodicule dimensions, shape and position), contrasting with consistent differences in leaf anatomy (macrohairs and cruciform silica bodies in the costal zone of the adaxial/abaxial leaf surfaces, crenate silica bodies on the abaxial leaf surface, lack of panicoid hairs on the abaxial leaf surface, bicellular microhairs and lobed papillae over the abaxial leaf surface, and sparse but elongated fusoid cells in the mesophyll of WA specimens) and in niche patterns. The anatomical/micromorphological characters suggest environmental adaptations to the Amazonian and ‘restinga’ forests, respectively. We therefore propose the segregation of the WA populations into a new species, Piresia tenella sp. nov. We provide a formal description, photographs, a line illustration, a distribution map and discussion of the conservation status for the new species.

Characterization and expression profile analysis of YABBY family genes in Pak-choi (Brassica rapa ssp. chinensis) under abiotic stresses and hormone treatments

YABBY proteins are widely distributed among different plant species and exhibit a higher degree of prevalence in angiosperms than in gymnosperms; abaxial cell fate in the lateral organs of plants is mainly determined by the functions of YABBY genes. However, to date, no scientific study has been conducted on the functions and responses of these genes under different forms of abiotic stresses in Pak-choi (Brassica rapa ssp. chinensis). In this study, we cloned and identified 12 YABBY family genes from Pak-choi. The evolutionary history of the YABBY genes was studied in nine species and showed that YABBY gene loss occurred during specific periods or in certain species during evolution. The putative YABBY family genes of Pak-choi were comprehensively analyzed by comparison with the corresponding orthologs in Arabidopsis and Chinese cabbage (Brassica rapa ssp. pekinensis) and classified into five subfamilies based on the specific protein domains and phylogenetic clades. A subcellular localization assay involving BcYABBY1b and BcYABBY2c confirmed that the BcYABBY proteins were localized in the nucleus. qRT-PCR data revealed that the BcYABBY genes are specifically expressed in distinct organs and developmental stages. Furthermore, the expression profiles of the BcYABBY genes were investigated under different hormone treatments and abiotic stress factors. In this study, we comprehensively identified and analyzed the YABBY gene family in the Pak-choi genome. Our data provide possible functional information regarding the involvement of BcYABBY genes in plant growth and development and in the response to abiotic stress and hormone treatments.

A biosystematic study of Euphorbia subgenus Chamaesyce (Euphorbiaceae) in Iran

We studied leaf anatomy, mitotic chromosomes and pollen grains of nine species of Euphorbia (E. chamaesyce, E. granulata, E. indica, E. humifusa, E. maculata, E. petiolata, E. prostrata, E. serpens and E. nutans) out of the 15 species of Euphorbia subg. Chamaesyce present in Iran. We compared our results with two species of subg. Esula sections Tythymalus and Helioscopia (E. peplus and E. helioscopia). Our anatomical survey identified the Kranz bundle sheath as a distinct anatomical character for subgenus Chamaesyce sect. Anisophyllum, differentiating this from E. petiolata of subg. Chamaesyce sect. Cheirolepidium. Based on type of abaxial epidermis cell walls, species were classified into three groups including species with zigzagged, sinuous and intermediate (zigzagged-sinuous) walls. Chromosome numbers for four species were reported for the first time from Iran, and 2n=32 is the first report for E. indica. Three shapes of pollen grains were determined: oblate spheroidal, prolate spheroidal and subprolate. A tectate perforate exine ornamentation was detected in almost all of the species.

Genome-Wide Study of YABBY Genes in Upland Cotton and Their Expression Patterns under Different Stresses.

Members of the YABBY gene family, a small plant-specific family of genes, have been proposed to function in specifying abaxial cell fate. Although to date little has been learned about cotton YABBY genes, completion of the cotton genome enables a comprehensive genome-wide analysis of YABBY genes in cotton. Here, a total of 12, 12, and 23 YABBY genes were identified in Gossypium arboreum (2n = 26, A2), G. raimondii (2n = 26, D5), and G. hirsutum (2n = 4x = 52, [AD]t), respectively. Sequence analysis showed that the N-terminal zinc-finger and C-terminal YABBY domains in YABBY proteins are highly conserved among cotton, Arabidopsis, and rice. Eighty-five genes from eight sequenced species naturally clustered into five groups, and the YAB2-like group could be divided into three sub-groups, indicating that YABBYs are highly conserved among the examined species. Orthologs from the At and Dt sub-genomes (where “t” indicates tetraploid) showed good collinearity, indicating that YABBY loci are highly conserved between these two sub-genomes. Whole-genome duplication was the primary cause of upland cotton YABBY gene expansion, segmental duplication played important roles in YABBY gene expansion within the At and Dt sub-genomes, and the YAB5-like group was mainly generated by segmental duplication. The long-terminal repeat retroelements Copia and Gypsy were identified as major transposable elements accompanying the appearance of duplicated YABBY genes, suggesting that transposable element expansion might be involved in gene duplication. Selection pressure analyses using PAML revealed that relaxed purifying selection might be the main impetus during evolution of YABBY genes in the examined species. Furthermore, exon/intron pattern and motif analyses indicated that genes within the same group were significantly conserved between Arabidopsis and cotton. In addition, the expression patterns in different tissues suggest that YABBY proteins may play roles in ovule development because YABBYs are highly expressed in ovules. The expression pattern of YABBY genes showed that approximately half of the YABBYs were down-regulated under different stress treatments. Collectively, our results represent a comprehensive genome-wide study of the YABBY gene family, which should be helpful in further detailed studies on the gene function and evolution of YABBY genes in cotton.

Ultrastructure effects of omethoate and cypermethrin insecticides on maize seedlings

ABSTRACTIncreasing studies suggest that insecticides are one of the plant stress elements that affect plant growth and productivity by interfering with cell metabolic and biochemical activities. Here, we show that the application of commonly used pesticides omethoate and cypermethrin on maize (Zea mays L. cv. Luyu 9) seedling leaves resulted in adverse effects on leaf ultrastructure changes under laboratory conditions. Electron microscopic studies reveal that the topical application of organophosphorus insecticide omethoate causes direct injury of leaf ultrastructures including cell wall breakdown of abaxial epidermis cells, inner cells, stomata guard cells; degradation of mitochondrial membrane, and chloroplast envelope membrane; and abnormal changes of lamella arrangement of chloroplast. And the topical application of cypermethrin insecticide causes plasmolysis of cells of the adaxial epidermis, mitochondrial cristae are degraded, and loosen arranged lamella of amyloplasts. All these changes indicated that omethoate and cypermethrin are stress factors that caused adverse effects on plant ultrastructures and biochemical molecules.

ASYMMETRIC LEAVES2-LIKE15 gene, a member of AS2/LOB family, shows a dual abaxializing or adaxializing function in Arabidopsis lateral organs

In determining leaf adaxial fates, Arabidopsis ASYMMERTIC LEAVES1 (AS1) and AS2/LBD6 are essential. The Arabidopsis ASYMMETRIC LEAVES2-LIKE15/LBD17 gene, one member of the LATERAL ORGAN BOUNDARY DOMAIN gene family, is expressed at the base of juvenile lateral roots, as well as in boundaries between meristems and organ primordial. For better comprehending the function of ASL15/LBD17 in the Arabidopsis development, its antisense-expression construct was constructed, and some 35S:ASL15/LBD17 transgenic plants that were antisense overexpression mutants were attained. The transgenic plants can specify either abaxial or adaxial cell fate in differently shaped rosette leaves. In detail, slightly and extremely narrow rosette leaves (class I) displayed abaxial cell traits, compared with those of Col-0. Inflorescence stems of these transgenic plants also showed abaxial organ identity. Both radial needle-like and filamentous symmetric rosette leaves (class II) presented adaxial cell fate, in contrast to those of wild type (Col-0). However, in the background of AS2 mutation, antisense 35S:ASL15 only presented abaxial organ identity, implying that the influences of antisense 35:ASL15 require a functional AS2 gene. In addition, antisense 35S:ASL15 was defective in proximodistal patterning. In addition, antisense 35S:ASL15 lead to the enhancement of the transcript levels of the KNOX genes, i.e., KNAT2, KNAT6, and STM, but not of the related KNAT1 gene. Taken together, our findings show that ASL15/LBD17 has a dual abaxializing or adaxializing function, and is also related to distal and proximal patterning in the lateral organs of Arabidopsis. Therefore, ASL15/LBD17 has multiple functions in the Arabidopsis development.

The rice YABBY4 gene regulates plant growth and development through modulating the gibberellin pathway.

YABBY genes encode seed plant-specific transcription factors that play pivotal roles in diverse aspects of leaf, shoot, and flower development. Members of the YABBY gene family are primarily expressed in lateral organs in a polar manner and function to specify abaxial cell fate in dicotyledons, but this polar expression is not conserved in monocotyledons. The function of YABBY genes is therefore not well understood in monocotyledons. Here we show that overexpression of the rice (Oryza sativa L.) YABBY4 gene (OsYABBY4) leads to a semi-dwarf phenotype, abnormal development in the uppermost internode, an increased number of floral organs, and insensitivity to gibberellin (GA) treatment. We report on an important role for OsYABBY4 in negative control of the expression of a GA biosynthetic gene by binding to the promoter region of the gibberellin 20-oxidase 2 gene (GA20ox2), which is a direct target of SLR1 (the sole DELLA protein negatively controlling GA responses in rice). OsYABBY4 also suppresses the expression level of SLR1 and interacts with SLR1 protein. The interaction inhibits GA-dependent degradation of SLR1 and therefore leads to GA insensitivity. These data together suggest that OsYABBY4 serves as a DNA-binding intermediate protein for SLR1 and is associated with the GA signaling pathway regulating gene expression during plant growth and development.