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LEUNIG (LUG) and LEUNIG_HOMOLOG (LUH) encode two closely related Arabidopsis proteins, belonging to the Gro/TLE family of transcriptional co-repressors. These two genes were previously shown to exhibit partially overlapping functions in embryo and flower development. In this report, the role of both LUH and LUG on seed mucilage extrusion was examined. Seed mucilage extrusion occurs after the seeds are imbibed, serving as functional aid in seed hydration, germination, and dispersal. While luh-1 mutants exhibited strong defects in seed mucilage extrusion, lug-3 mutants exhibited a minor phenotype in mucilage extrusion. Further characterization indicates that luh-1 does not exhibit any obvious defect in seed epidermal cell differentiation, mucilage synthesis, or mucilage deposition, suggesting a specific role of LUH in mucilage extrusion. This seed mucilage phenotype of luh-1 is identical to that of mucilage modified 2 (mum2) mutants. MUM2 encodes a β-galactosidase required for the modification of the mucilage. Quantitative reverse transcription polymerase chain reaction of RNA extracted from siliques detected a slight decrease of MUM2 mRNA in the luh-1 mutant compared to the wild type. Together, LUH and possibly LUG may specifically regulate mucilage extrusion by promoting the expression of genes required for mucilage maturation.

Microscopic imaging of fluorescent reporters for key meristem regulators in live tissues is emerging as a powerful technique, enabling researchers to observe dynamic spatial and temporal distribution of hormonal and developmental regulators in living cells. Aided by time-lapse microphotography, new types of imaging acquisition and analysis software, and computational modeling, we are gaining significant insights into shoot apical meristem (SAM) behavior and function. This review is focused on summarizing recent advances in the understanding of SAM organization, development, and behavior derived from live-imaging techniques. This includes the revelation of mechanical forces in microtubule-controlled anisotropic growth, the role of the CLV-WUS network in the specification of peripheral zone and central zone cells, the multiple feedback loops involving cytokinin in controlling WUS expression, auxin dynamics in determining the position of new primordia, and, finally, sequence of regulatory events leading to de novo assembly of shoots from callus in culture. Future studies toward formulating "digital SAM" that incorporates multi-dimensional data ranging from images of SAM morphogenesis to a genome-scale expression map of SAM will greatly enhance our ability to understand, predict, and manipulate SAM, containing the stem cells that give rise to all above ground parts of a plant.

LEUNIG (LUG) and LEUNIG_HOMOLOG (LUH) encode two closely related Arabidopsis proteins, belonging to the Gro/TLE family of transcriptional co-repressors. These two genes were previously shown to exhibit partially overlapping functions in embryo and flower development. In this report, the role of both LUH and LUG on seed mucilage extrusion was examined. Seed mucilage extrusion occurs after the seeds are imbibed, serving as functional aid in seed hydration, germination, and dispersal. While luh-1 mutants exhibited strong defects in seed mucilage extrusion, lug-3 mutants exhibited a minor phenotype in mucilage extrusion. Further characterization indicates that luh-1 does not exhibit any obvious defect in seed epidermal cell differentiation, mucilage synthesis, or mucilage deposition, suggesting a specific role of LUH in mucilage extrusion. This seed mucilage phenotype of luh-1 is identical to that of mucilage modified 2 (mum2) mutants. MUM2 encodes a β-galactosidase required for the modification of the mucilage. Quantitative reverse transcription polymerase chain reaction of RNA extracted from siliques detected a slight decrease of MUM2 mRNA in the luh-1 mutant compared to the wild type. Together, LUH and possibly LUG may specifically regulate mucilage extrusion by promoting the expression of genes required for mucilage maturation.