Carbohydrate import into seeds directly determines seed size and must have been increased through domestication. However, evidence of the domestication of sugar translocation and the identities of ...seed-filling transporters have been elusive. Maize ZmSWEET4c, as opposed to its sucrose-transporting homologs, mediates transepithelial hexose transport across the basal endosperm transfer layer (BETL), the entry point of nutrients into the seed, and shows signatures indicative of selection during domestication. Mutants of both maize ZmSWEET4c and its rice ortholog OsSWEET4 are defective in seed filling, indicating that a lack of hexose transport at the BETL impairs further transfer of sugars imported from the maternal phloem. In both maize and rice, SWEET4 was likely recruited during domestication to enhance sugar import into the endosperm.
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IJS, NUK, SBMB, UL, UM, UPUK
The post-translational addition of SUMO plays essential roles in numerous eukaryotic processes including cell division, transcription, chromatin organization, DNA repair, and stress defense through ...its selective conjugation to numerous targets. One prominent plant SUMO ligase is METHYL METHANESULFONATE-SENSITIVE (MMS)-21/HIGH-PLOIDY (HPY)-2/NON-SMC-ELEMENT (NSE)-2, which has been connected genetically to development and endoreduplication. Here, we describe the potential functions of MMS21 through a collection of UniformMu and CRISPR/Cas9 mutants in maize (Zea mays) that display either seed lethality or substantially compromised pollen germination and seed/vegetative development. RNA-seq analyses of leaves, embryos, and endosperm from mms21 plants revealed a substantial dysregulation of the maize transcriptome, including the ectopic expression of seed storage protein mRNAs in leaves and altered accumulation of mRNAs associated with DNA repair and chromatin dynamics. Interaction studies demonstrated that MMS21 associates in the nucleus with the NSE4 and STRUCTURAL MAINTENANCE OF CHROMOSOMES (SMC)-5 components of the chromatin organizer SMC5/6 complex, with in vitro assays confirming that MMS21 will SUMOylate SMC5. Comet assays measuring genome integrity, sensitivity to DNA-damaging agents, and protein versus mRNA abundance comparisons implicated MMS21 in chromatin stability and transcriptional controls on proteome balance. Taken together, we propose that MMS21-directed SUMOylation of the SMC5/6 complex and other targets enables proper gene expression by influencing chromatin structure.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Abstract
Functional and architectural diversification of transcription factor families has played a central role in the independent evolution of complex development in plants and animals. Here, we ...investigate the role of architectural constraints on evolution of B3 DNA binding domains that regulate plant embryogenesis. B3 domains of ABI3, FUS3, LEC2 and VAL1 proteins recognize the same cis-element. Complex architectures of ABI3 and VAL1 integrate cis-element recognition with other signals, whereas LEC2 and FUS3 have reduced architectures conducive to roles as pioneer activators. In yeast and plant in vivo assays, B3 domain functions correlate with architectural complexity of the parent transcription factor rather than phylogenetic relatedness. In a complex architecture, attenuated ABI3-B3 and VAL1-B3 activities enable integration of cis-element recognition with hormone signaling, whereas hyper-active LEC2-B3 and FUS3-B3 over-ride hormonal control. Three clade-specific amino acid substitutions (β4-triad) implicated in interactions with the DNA backbone account for divergence of LEC2-B3 and ABI3-B3. We find a striking correlation between differences in in vitro DNA binding affinity and in vivo activities of B3 domains in plants and yeast. Our results highlight the role of DNA backbone interactions that preserve DNA sequence specificity in adaptation of B3 domains to functional constraints associated with domain architecture.
The transition between seed and seedling phases of development is coordinated by an interaction between the closely related ABSCISIC ACID-INSENSITIVE3 (ABI3), FUSCA3 (FUS3), and LEAFY COTYLEDON2 ...(LEC2; AFL) and VIVIPAROUS1 / ABI3-LIKE (VAL) clades of the B3 transcription factor family that respectively activate and repress the seed maturation program. In the val1 val2 double mutant, derepression of the LEC1, LEC1-LIKE (L1L), and AFL (LAFL) network is associated with misexpression of embryonic characteristics resulting in arrested seedling development. We show that while the frequency of the embryonic fate in val1 val2 seedlings depends on the developmental timing of seed rescue, VAL proteins repress LAFL genes during germination, but not during seed development. Quantitative analysis of LAFL mutants that suppress the val1 val2 seedling phenotype revealed distinct roles of LAFL genes in promoting activation of the LAFL network. LEC2 and FUS3 are both essential for coordinate activation of the network, whereas effects of LEC1, L1L, and ABI3 are additive. Suppression of the val1 val2 seedling phenotype by the B3 domain-deficient abi3-12 mutation indicates that ABI3 activation of the LAFL network requires the B3 DNA-binding domain. In the VAL-deficient background, coordinate regulation of the LAFL network is observed over a wide range of genetic and developmental conditions. Our findings highlight distinct functional roles and interactions of LAFL network genes that are uncovered in the absence of VAL repressors.
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Two subfamilies of plant-specific B3 domain transcription factors regulate the fundamental transition between seed and vegetative phases of development. The AFL B3 genes activate the embryo ...maturation program, while the closely related VAL B3 genes shutdown the AFL network before germination. VP8/AMP1 signaling most probably acts upstream of the AFL network. Key downstream AFL targets elaborate seed-specific abscisic acid (ABA), gibberellin (GA), and auxin signaling. ABA feeds back into network via ABI3 interaction with ABI5. GA promotes repression of the AFL network by the VAL repressors and the PICKLE (PKL) chromatin-remodeling factor before germination. Strikingly, the functional symmetry of the AFL and VAL B3 genes is mirrored in patterns of chromatin modification.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Genetic networks that determine rates of organ initiation and organ size are key regulators of plant architecture. Whereas several genes that influence the timing of lateral organ initiation have ...been identified, the regulatory pathways in which these genes operate are poorly understood. Here, we identify a class of genes implicated in regulation of the lateral organ initiation rate. Loss-of-function mutations in the MATE transporter encoded by maize (Zea mays) Big embryo 1 (Bige1) cause accelerated leaf and root initiation as well as enlargement of the embryo scutellum. BIGE1 is localized to trans-Golgi, indicating a possible role in secretion of a signaling molecule. Interestingly, phenotypes of bige1 bear striking similarity to cyp78a mutants identified in diverse plant species. We show that a CYP78A gene is upregulated in bige1 mutant embryos, suggesting a role for BIGE1 in feedback regulation of a CYP78A pathway. We demonstrate that accelerated leaf formation and early flowering phenotypes conditioned by mutants of Arabidopsis thaliana BIGE1 orthologs are complemented by maize Bige1, showing that the BIGE1 transporter has a conserved function in regulation of lateral organ initiation in plants. We propose that BIGE1 is required for transport of an intermediate or product associated with the CYP78A pathway.
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Nearly all eukaryotes carry DNA transposons of the Robertson's
(
) superfamily, a widespread source of genome instability and genetic variation. Despite their pervasive impact on host genomes, much ...remains unknown about the evolution of these transposons. Transposase recognition of terminal inverted repeats (TIRs) is thought to drive and constrain coevolution of
transposase genes and TIRs. To address the extent of this relationship and its impact, we compared separate phylogenies of TIRs and
gene sequences from
elements in the maize genome. Five major clades were identified. As expected, most
elements were bound by highly similar TIRs from the same clade (homomorphic type). However, a subset of elements contained dissimilar TIRs derived from divergent clades. These "heteromorphs" typically occurred in multiple copies indicating active transposition in the genome. In addition, analysis of internal sequences showed that exchanges between elements having divergent TIRs produced new
and
gene combinations. In several instances, TIR homomorphs had been regenerated within a heteromorph clade with retention of distinctive internal
sequence combinations. Results reveal that recombination between divergent clades facilitates independent evolution of transposase (
), transposase-binding targets (TIRs), and capacity for insertion (
) of active
elements. This mechanism would be enhanced by the preference of
insertions for recombination-rich regions near the 5' ends of genes. We suggest that cycles of recombination give rise to alternating homo- and heteromorph forms that enhance the diversity on which selection for
fitness can operate.
In the seed, a fundamental transition between embryo and vegetative phases of plant development is coordinated by the interaction between the AFL and VAL sub‐clades of the plant specific B3 domain ...transcription factor family. The AFL B3 factors together with LEC1‐type HAP3 transcription factors promote embryo maturation; whereas the VAL B3 factors repress the LEC1/AFL (LAFL) network during seed germination. Recent advances reveal that genes in key developmental programs and hormone signaling pathways are downstream targets of the LAFL network highlighting the central role of the LAFL network in integration of intrinsic developmental and hormonal signals during plant development. The VAL B3 proteins are proposed to mediate repression by recruiting a histone deacetylase complex (HDAC) to LAFL genes that contain the Sph/RY cis‐element recognized by AFL and VAL B3‐DNA‐binding domains. In addition to VAL B3 factors, epigenetic mechanisms are implicated in maintaining repression of LAFL network during vegetative development. WIREs Dev Biol 2014, 3:135–145. doi: 10.1002/wdev.126
This article is categorized under:
Plant Development > Fertilization, Embryogenesis, and Seed Development
Plant Development > Vegetative Development
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
In many organisms, various enzymes mediate site-specific carotenoid cleavage to generate biologically active apocarotenoids. These carotenoid-derived products include provitamin A, hormones, and ...flavor and fragrance molecules. In plants, the CCD1 enzyme cleaves carotenoids at 9,10 (9′,10′) bonds to generate multiple apocarotenoid products. Here we systematically analyzed volatile apocarotenoids generated by maize CCD1 (ZmCCD1) from multiple carotenoid substrates. ZmCCD1 did not cleave geranylgeranyl diphosphate or phytoene but did cleave other linear and cyclic carotenoids, producing volatiles derived from 9,10 (9′,10′) bond cleavage. Additionally the Arabidopsis, maize, and tomato CCD1 enzymes all cleaved lycopene to generate 6-methyl-5-hepten-2-one. 6-Methyl-5-hepten-2-one, an important flavor volatile in tomato, was produced by cleavage of the 5,6 or 5′,6′ bond positions of lycopene but not geranylgeranyl diphosphate, ζ-carotene, or phytoene. In vitro, ZmCCD1 cleaved linear and cyclic carotenoids with equal efficiency. Based on the pattern of apocarotenoid volatiles produced, we propose that CCD1 recognizes its cleavage site based on the saturation status between carbons 7 and 8 (7′ and 8′) and carbons 11 and 12 (11′ and 12′) as well as the methyl groups on carbons 5, 9, and 13 (5′, 9′, and 13′).
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The maize (Zea mays) gibberellin (GA)-deficient mutant dwarfl (d1) displays dwarf ism and andromonoecy (i.e. forming anthers in the female flower). Previous characterization indicated that the d1 ...mutation blocked three steps in GA biosynthesis; however, the locus has not been isolated and characterized. Here, we report that D1 encodes a GA 3-oxidase catalyzing the final step of bioactive GA synthesis. Recombinant D1 is capable of converting GA₂₀ to GA₁, G₂₀ to GA₃, GA₅ to GA₃, and GA₉ to GA₄ in vitro. These reactions are widely believed to take place in the cytosol. However, both in vivo GFP fusion analysis and westernblot analysis of organelle fractions using a D1-specific antibody revealed that the D1 protein is dual localized in the nucleus and cytosol. Furthermore, the upstream gibberellin 20-oxidasel (ZmGA20ox1) protein was found dual localized in the nucleus and cytosol as well. These results indicate that bioactive GA can be synthesized in the cytosol and the nucleus, two compartments where GA receptor Gibberellin-insensitive dwarf proteinl exists. Furthermore, the D1 protein was found to be specifically expressed in the stamen primordia in the female floret, suggesting that the suppression of stamen development is mediated by locally synthesized GAs.
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