In plants the dorsoventral boundary of leaves defines an axis of symmetry through the centre of the organ separating the top (dorsal) and bottom (ventral) tissues. Although the positioning of this boundary is critical for leaf morphogenesis, how the boundary is established and how it influences development remains unclear. Using live-imaging and perturbation experiments we show that leaf orientation, morphology and position are pre-patterned by HD-ZIPIII and KAN gene expression in the shoot, leading to a model in which dorsoventral genes coordinate to regulate plant development by localizing auxin response between their expression domains. However we also find that auxin levels feedback on dorsoventral patterning by spatially organizing HD-ZIPIII and KAN expression in the shoot periphery. By demonstrating that the regulation of these genes by auxin also governs their response to wounds, our results also provide a parsimonious explanation for the influence of wounds on leaf dorsoventrality.

Background: Light is an important factor for plant growth and development. Results: GBF1 interacts with two other bZIP proteins, HY5 and HYH, in light signaling. Conclusion: This work demonstrates the functional interconnections of GBF1, HY5, and HYH. Significance: The knowledge gained in this study will help to understand light-controlled plant growth and development.

A defining feature of plant leaves is their flattened shape. This shape depends on an antagonism between the genes that specify adaxial (top) and abaxial (bottom) tissue identity; however, the molecular nature of this antagonism remains poorly understood. Class III homeodomain leucine zipper (HD-ZIP) transcription factors are key mediators in the regulation of adaxial-abaxial patterning. Their expression is restricted adaxially during early development by the abaxially expressed microRNA (MIR)165/166, yet the mechanism that restricts MIR165/166 expression to abaxial leaf tissues remains unknown. Here, we show that class III and class II HD-ZIP proteins act together to repress MIR165/166 via a conserved cis-element in their promoters. Organ morphology and tissue patterning in plants, therefore, depend on a bidirectional repressive circuit involving a set of miRNAs and its targets. T he morphogenesis of lateral organs in plants and animals is dependent on the specification of distinct cell types early in development. In particular, the correct patterning of adaxialabaxial tissues in plant organs such as leaves is critical for the generation of a lamina shape and the formation of a polar vascular system (1-4). Adaxial-abaxial cell-type patterning in turn depends on the restricted expression of several genes known to specify these cell types, including the class III homeodomain leucine zipper genes (HD-ZIPIIIs), KANADI genes, HD-ZIPIIs, and microRNA (MIR)165/166 (1, 2, 4-11). In general, genetic analyses have indicated that adaxial and abaxial factors act oppositely in organ patterning (1,2,4,(8)(9)(10)(11). Hence, loss-of-function mutations in genes promoting adaxial cell identity typically cause an abaxialized phenotype that correlates with the ectopic expression of abaxial genes, whereas loss-of-function mutations in abaxial genes produce an adaxialized phenotype that is accompanied by the expanded expression of adaxial genes. This antagonistic interaction between adaxial and abaxial factors may be mediated by mutually antagonistic regulation (12) or through opposing regulation of common targets (9, 13-16).A key set of transcription factors involved in plant organ polarity are the HD-ZIPIII proteins, such as REVOLUTA (REV), which specify adaxial cell fate (1, 2, 4, 17). The expression of these genes is restricted specifically to adaxial tissues via the action of two miRNA families, MIR165 and MIR166 (2, 7). In turn, the expression of these miRNAs is restricted to abaxial tissues and this restriction is essential for maintaining proper organ polarity (18).Here, we address the question of how MIR165/166 are regulated. We show that the HD-ZIPII proteins HAT3 and ATHB4 physically interact with HD-ZIPIII proteins and directly repress MIR165/166 expression via a conserved cis-element located in their promoters. This regulatory interaction largely accounts for HAT3 and ATHB4 function and reveals the molecular nature of a bidirectional repressive circuit essential to maintain balance between adaxial and abaxial tissue sp...

Abstract:In plants the dorsoventral boundary of leaves defines an axis of symmetry 22 through the centre of the organ separating the top (dorsal) and bottom (ventral) tissues. 23Although the positioning of this boundary is critical for leaf morphogenesis, how the 24 boundary is established and how it influences development remains unclear. Using live-25 imaging and perturbation experiments we show that leaf orientation, morphology and 26 position are pre-patterned by HD-ZIPIII and KAN gene expression in the shoot, leading 27 to a model in which dorsoventral genes coordinate to regulate plant development by 28 localizing auxin response between their expression domains. However we also find that 29 auxin levels feedback on dorsoventral patterning by spatially organizing HD-ZIPIII and 30

Arabidopsis GBF1/ZBF2 is a bZIP transcription factor that plays dual but opposite regulatory roles in cryptochrome-mediated blue light signaling. Here, we show the genetic and molecular interrelation of GBF1 with two well characterized negative regulators of light signaling, COP1 and SPA1, in photomorphogenic growth and light-regulated gene expression. Our results further reveal that GBF1 protein is less abundant in the darkgrown seedlings and is degraded by a proteasome-mediated pathway independent of COP1 and SPA1. Furthermore, COP1 physically interacts with GBF1 and is required for the optimum accumulation of GBF1 protein in light-grown seedlings. Taken together, this study provides a mechanistic view of concerted function of three important regulators in Arabidopsis seedling development.