knox genes encode homeodomain-containing transcription factors that are required for meristem maintenance and proper patterning of organ initiation. In plants with simple leaves, knox genes are expressed exclusively in the meristem and stem, but in dissected leaves, they are also expressed in leaf primordia, suggesting that they may play a role in the diversity of leaf form. This hypothesis is supported by the intriguing phenotypes found in gain-of-function mutations where knox gene misexpression affects leaf and petal shape. Similar phenotypes are also found in recessive mutations of genes that function to negatively regulate knox genes. KNOX proteins function as heterodimers with other homeodomains in the TALE superclass. The gibberellin and lignin biosynthetic pathways are known to be negatively regulated by KNOX proteins, which results in indeterminate cell fates.

Sequential metabolic enzymes in glucose metabolism have long been hypothesized to form multienzyme complexes that regulate glucose flux in living cells. However, it has been challenging to directly observe these complexes and their functional roles in living systems. In this work, we have used wide-field and confocal fluorescence microscopy to investigate the spatial organization of metabolic enzymes participating in glucose metabolism in human cells. We provide compelling evidence that human liver-type phosphofructokinase 1 (PFKL), which catalyzes a bottleneck step of glycolysis, forms various sizes of cytoplasmic clusters in human cancer cells, independent of protein expression levels and of the choice of fluorescent tags. We also report that these PFKL clusters colocalize with other rate-limiting enzymes in both glycolysis and gluconeogenesis, supporting the formation of multienzyme complexes. Subsequent biophysical characterizations with fluorescence recovery after photobleaching and FRET corroborate the formation of multienzyme metabolic complexes in living cells, which appears to be controlled by post-translational acetylation on PFKL. Importantly, quantitative high-content imaging assays indicated that the direction of glucose flux between glycolysis, the pentose phosphate pathway, and serine biosynthesis seems to be spatially regulated by the multienzyme complexes in a cluster-size-dependent manner. Collectively, our results reveal a functionally relevant, multienzyme metabolic complex for glucose metabolism in living human cells.

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Maize (Zea mays) leaves provide a useful system to study how proximal/distal patterning is established because of the distinct tissues found in the distal blade and the proximal sheath. Several mutants disrupt this pattern, including the dominant knotted1-like homeobox (knox) mutants. knox genes encode homeodomain proteins of the TALE superclass of transcription factors. Class I knox genes are expressed in the meristem and down-regulated as leaves initiate. Gain-of-function phenotypes result from misexpression in leaves. We identified a new dominant allele of maize knotted1, Kn1-DL, which contains a transposon insertion in the promoter in addition to a tandem duplication of the kn1 locus. In situ hybridization shows that kn1 is misexpressed in two different parts of the blade that correlate with the different phenotypes observed. When kn1 is misexpressed along the margins, flaps of sheath-like tissue form along the margins. Expression in the distal tip leads to premature termination of the midrib into a knot and leaf bifurcation. The gain-of-function phenotypes suggest that kn1 establishes proximal/distal patterning when expressed in distal locations and lead to the hypothesis that kn1 normally participates in the establishment of proximal/distal polarity in the incipient leaf.Plants produce organs throughout their life span from meristems, groups of self-renewing cells whose derivatives become the roots and shoots of a plant (Veit, 2006). The shoot apical meristem (SAM) initiates the leaves and stem, while the root apical meristem is responsible for generating the root system. The SAM initiates leaves in a defined pattern, called phyllotaxy, and at defined intervals, referred to as plastochrons. A leaf in plastochron 1 (P 1 ) has just emerged from the meristem, while a P 2 leaf is one plastochron older. From observing the position of these leaf primordia, one can predict the position of the next leaf (P 0 ) while it is still part of the meristem. Given that meristem cells are indeterminate and leaf cells are determinate, a major question in plant biology is how cell fate changes during the transitions from meristem to P 0 and then to leaf.In the last decade, a number of genes have been identified that are expressed in meristems and not in leaves and thus provide insight into the process of leaf initiation. The class I knotted1-like homeobox (knox) genes are expressed throughout the SAM except in the P 0 cells (Jackson et al., 1994). It has been hypothesized that down-regulation of knox genes at P 0 is required for leaf initiation. Indeed, in species with dissected leaves where knox genes are expressed in leaves, knox down-regulation still occurs in the P 0 (Hay and Tsiantis, 2006;Champagne et al., 2007). The importance of knox genes for plant development is highlighted by loss-of-function mutants. Plants carrying mutations in the Arabidopsis (Arabidopsis thaliana) SHOOT MERISTEMLESS gene terminate after the cotyledons form, and further growth occurs from adventitious meristems that may also terminate (Long et a...