Requirement of KNAT1/BP for the Development of Abscission Zones in Arabidopsis thaliana

The KNAT1 gene is a member of the Class I KNOXhomeobox gene family and is thought to play an important role in meristem development and leaf morphogenesis. Recent studies have demonstrated that KNAT1/BP regulates the architecture of the inflorescence by affecting pedicle development in Arabidopsis thaliana. Herein, we report the characterization of an Arabidopsis T-DNA insertion mutant that shares considerable phenotypic similarity to the previously identified mutant brevipedicle （bp）. Molecular and genetic analyses showed that the mutant is allelic to bp and that the T-DNA is located within the first helix of the KNAT1 homeodomain （HD）. Although the mutation causes a typical abnormality of short pedicles, propendent siliques, and semidwarfism, no obvious defects are observed in the vegetative stage. A study on cell morphology showed that asymmetrical division and inhibition of cell elongation contribute to the downward-pointing and shorter pedicle phenotype. Loss of KNAT/BPfunction results in the abnormal development of abscission zones. Mlcroarray analysis of gene expression profiling suggests that KNAT1/BP may regulate abscission zone development through hormone signaling and hormone metabolism in Arabidopsis.     

Retarded Embryo Development 1(RED1) regulates embryo development,seed maturation and plant growth in Arabidopsis

Plant seeds accumulate large amounts of protein and carbohydrate as storage reserves during maturation.Thus,understanding the genetic control of embryo and seed development may provide bioengineering tools for yield improvement.In this study,we report the identification of Retarded Embryo Development 1(RED1) gene in Arabidopsis,whose two independent T-DNA insertion mutant lines,SALK_085642(red1-1) and SALK_022583(red1-2),show a retarded embryo development phenotype.The embryogenesis process ceases at the late heart stage in red 1-1 and at the bent-cotyledon stage in red 1-2,respectively,resulting in seed abortion in both lines.The retarded embryo development and seed abortion phenotypes reverted to normal when RED1 complementation constructs were introduced into mutant plants.Small red 1-2 homozygous plants can be successfully rescued by culturing immature seeds,indicating that seed abortion likely results from compromised tolerance to the desiccation process associated with seed maturation.Consistent with this observation,red 1-2 seeds accumulate less protein,and the expression of two late embryo development reporter transgenes,LEA::GUS and β-conglycinin::GUS,was significantly weak and started relatively late in the red 1-2 mutant lines compared to the wild type.The RED1 gene encodes a plant specific novel protein that is localized in the nucleus.These results indicate that RED1 plays important roles in embryo development,seed maturation and plant growth.     

GAMETOPHYTIC FACTOR 1, Involved in Pre-mRNA Splicing,Is Essential for Megagametogenesis and Embryogenesis in Arabidopsis

RNA biogenesis is essential and vital for accurate expression of genes. It is obvious that cells cannot continue normal metabolism when RNA splicing is interfered with. sgt13018 is such a mutant, with partial loss of function of GAMETOPHYTIC FACTOR 1 （GFA1）; a gene likely involved in RNA biogenesis in Arabidopsis. The mutant is featured in the phenotype of diminished female gametophyte development at stage FG5 and is associated with the arrest of early embryo development in Arabidopsis. Bioinformatics data showed that homologs of gene GFA1 in yeast and human encode putative U5 snRNPspecific proteins required for pre-mRNA splicing. Furthermore, the result of yeast two-hybrid assay indicated that GFA1 physically interacted with AtBrr2 and AtPrp8, the putative U5 snRNP components, of Arabidopsis. This investigation suggests that GFA1 is involved in mRNA biogenesis through interaction with AtBrr2 and AtPrp8 and functions in megagametogenesis and embryogenesis in plant.     

Oil Body Biogenesis during Brassica napus Embryogenesis

Although the oil body is known to be an important membrane enclosed compartment for oil storage in seeds, we have little understanding about its biogenesis during embryogenesis. In the present study we investigated the oil body emergence and variations in Brassica napus cv. Topas. The results demonstrate that the oil bodies could be detected already at the heart stage, at the same time as the embryos began to turn green, and the starch grains accumulated in the chloroplast stroma. In comparison, we have studied the development of oil bodies between Arabidopsis thaliana wild type （Col） and the low-seed-oil mutant wrinkled1-3. We observed that the oil body development in the embryos of Col is similar to that of B. napus cv. Topas, and that the size of the oil bodies was obviously smaller in the embryos of wrinkled1-3. Our results suggest that the oil body biogenesis might be coupled with the embryo chloroplast.     

Identification of a delayed leaf greening gene from a mutation of pummelo

Delayed greening of young leaves is an unusual phenomenon of plants in nature. Citrus are mostly evergreen tree species. Here, a natural mutant of “Guanxi” pummelo(Citrus maxima), which shows yellow leaves at the young stage, was characterized to identify the genes underlying the trait of delayed leaf greening in plants. A segregating population with this mutant as the seed parent and a normal genotype as the pollen parent was generated. Two DNA pools respectively from the leaves of segregating seedlings with extreme phenotypes of normal leaf greening and delayed leaf greening were collected for sequencing. Bulked segregant analysis(BSA) and In Del marker analysis demonstrated that the delayed leaf greening trait is governed by a 0.3 Mb candidate region on chromosome 6. Gene expression analysis further identified a key candidate gene(Citrus Delayed Greening gene 1, CDG1) in the 0.3 Mb region, which showed significantly differential expression between the genotypes with delayed and normal leaf greening phenotypes. There was a 67 bp In Del region difference in the CDG1 promoter and the In Del region contains a TATA-box element. Confocal laser-scanning microscopy revealed that the CDG1-GFP fusion protein signals were co-localized with the chloroplast signals in the protoplasts. Overexpression of CDG1 in tobacco and Arabidopsis led to the phenotype of delayed leaf greening. These results suggest that the CDG1 gene is involved in controlling the delayed leaf greening phenotype with important functions in chloroplast development.     

BUD2, encoding an S-adenosylmethionine decarboxylase, is required for Arabidopsis growth and development

Polyamines are implicated in regulating various developmental processes in plants, but their exact roles and how they govern these processes still remain elusive. We report here an Arabidopsis bushy and dwarf mutant, bud2, which results from the complete deletion of one member of the small gene family that encodes S-adenosylmethionine decarboxylases （SAMDCs） necessary for the formation of the indispensable intermediate in the polyamine biosynthetic pathway. The bud2 plant has enlarged vascular systems in inflorescences, roots, and petioles, and an altered homeostasis ofpolyamines. The double mutant of bud2 and samdcl, a knockdown mutant of another SAMDC member, is embryo lethal, demonstrating that SAMDCs are essential for plant embryogenesis. Our results suggest that polyamines are required for the normal growth and development of higher plants.     

PIF3 Is Involved in the Primary Root Growth Inhibition of Arabidopsis Induced by Nitric Oxide in the Light

PHYTOCHROME INTERACTING FACTOR3 （PIF3） is an important component in the phytochrome signaling pathway and mediates plant responses to various environmental conditions. We found that PIF3 is involved in the inhibition of root growth of Arabidopsis thaliana seedlings induced by nitric oxide （NO） in light. Overexpression of PIF3 partially alleviated the inhibitory effect of NO on root growth, whereas the pif3-1 mutant displayed enhanced sensitivity to NO in terms of root growth. During phytochrome signaling, the photoreceptor PHYB mediates the degradation of PIF3. We found that the phyB-9 mutant had a similar phenotype to that of PIF3ox in terms of responsiveness to NO. Furthermore, NO treatment promoted the accumulation of PHYB, and thus reduced PIF3 content. Our results further show that the activity of PIF3 is regulated by the DELLA protein RGL3[RGA （repressor of gal-3） LIKE 3]. Therefore, we speculate that PIF3 lies downstream of PHYB and RGL3, and plays an important role in the inhibitory effect of NO on root growth of Arabidopsis seedlings in light.     

Retromer Subunits VPS35A and VPS29 Mediate Prevacuolar Compartment （PVC） Function in Arabidopsis

Intracellular protein routing is mediated by vesicular transport which is tightly regulated in eukaryotes. The protein and lipid homeostasis depends on coordinated delivery of de novo synthesized or recycled cargoes to the plasma membrane by exocytosis and their subsequent removal by rerouting them for recycling or degradation. Here, we report the characterization of protein affected trafficking 3 （pat3） mutant that we identified by an epifluorescence-based for- ward genetic screen for mutants defective in subcellular distribution of Arabidopsis auxin transporter PIN1-GFR While pat3 displays largely normal plant morphology and development in nutrient-rich conditions, it shows strong ectopic intracellular accumulations of different plasma membrane cargoes in structures that resemble prevacuolar compart- ments （PVC） with an aberrant morphology. Genetic mapping revealed that pat3 is defective in vacuolar protein sorting 35A （VPS35A）, a putative subunit of the retromer complex that mediates retrograde trafficking between the PVC and trans-Golgi network. Similarly, a mutant defective in another retromer subunit, vps29, shows comparable subcellular defects in PVC morphology and protein accumulation. Thus, our data provide evidence that the retromer components VPS35A and VPS29 are essential for normal PVC morphology and normal trafficking of plasma membrane proteins in plants. In addition, we show that, out of the three VPS35 retromer subunits present in Arabidopsis thaliana genome, the VPS35 homolog A plays a prevailing role in trafficking to the lyric vacuole, presenting another level of complexity in the retromer-dependent vacuolar sorting.     

Camouflage Patterning in Maize Leaves Results from a Defect in Porphobilinogen Deaminase

Maize leaves are produced from polarized cell divisions that result in clonal cell lineages arrayed along the long axis of the leaf. We utilized this stereotypical division pattern to identify a collection of mutants that form chloroplast pigmentation sectors that violate the clonal cell lineages. Here, we describe the camouflage1 （cfl） mutant, which develops nonclonal, yellow-green sectors in its leaves. We cloned the cfl gene by transposon tagging and determined that it encodes porphobilinogen deaminase （PBGD）, an enzyme that functions early in chlorophyll and heme biosynthesis. While PBGD has been characterized biochemically, no viable mutations in this gene have been reported in plants. To investigate the in vivo function of PBGD, we characterized the cfl mutant. Histological analyses revealed that cfl yellow sectors display the novel phenotype of bundle sheath cell-specific death. Light-shift experiments determined that constant light suppressed cfl sector formation, a dark/light transition is required to induce yellow sectors, and that sectors form only during a limited time of leaf development. Biochemical experiments determined that of 1 mutant leaves have decreased PBGD activity and increased levels of the enzyme substrate in both green and yellow regions. Furthermore, the cfl yellow regions displayed a reduction in catalase activity. A threshold model is hypothesized to explain the cfl variegation and incorporates photosynthetic cell differentiation, reactive oxygen species scavenging, and PBGD function.     

An Arabidopsis embryonic lethal mutant with reduced expression of alanyl—t RNA synthetase gene

In present paper,one of the T-DNA insertional embryonic lethal mutant of Arabidopsis is identified and designated as acd mutant.The embryo developmant of this mutant is arrested in globular stage,The cell division pattern is abnormal during early embryogenesis and results in distubed cellular differentiation.Most of mutant embryos are finally degenerated and aborted in globular stage,However,a few of them still can germinate in agar palte and produce seedlings with shoter hypoctyl and distorted shoot meristem.To understand the molecular basis of the phenotype of this mutant,the joint fragment of T-DNA/plant DNA is isolated by plasmid rescue and Dig-labeled as probe for cDNA library screening.According to the sequence analysis and similarity searching,a 936 bp cDNA sequence(EMBL accession #:Y12555)from selectoed positive clone shows a 99.8%(923/925bp) sequence homolgy with Alanyl-tRNA Synthetase(AlaRS) gene of Arabidopsis thaliana.Furthermore,the data of in situ hybridization experiment indicate that the expression of Ala RS gene is weak in early embryogenesis and declines along with globular embryodevelopment in this mutant Accordingly,the reduced expression of Ala RS gene may be closely related to the morphological changes in early embryogenesis of this lethal mutant.     

Role of Arabidopsis UV RESISTANCE LOCUS 8 in Plant Growth Reduction under Osmotic Stress and Low Levels of UV-B

In high-light environments, plants are exposed to different types of stresses, such as an excess of UV-B, but also drought stress which triggers a common morphogenic adaptive response resulting in a general reduction of plant growth. Here, we report that the Arabidopsis thaliana UVRESISTANCE LOCUS 8 （UVR8） gene, a known regulator of the UV-B morphogenic response, was able to complement a Saccharomyces cerevisiae osmo-sensitive mutant and its expression was induced after osmotic or salt stress in Arabidopsis plants. Under low levels of UV-B, plants overexpressing UVR8 are dwarfed with a reduced root development and accumulate more flavonoids compared to control plants. The growth defects are mainly due to the inhibition of cell expansion. The growth inhibition triggered by UVR8 overexpression in plants under low levels of UV-B was exacerbated by mannitol-induced osmotic stress, but it was not significantly affected by ionic stress. In contrast, uvr8-6 mutant plants do not differ from wild-type plants under standard conditions, but they show an increased shoot growth under high-salt stress. Our data suggest that UVR8-mediated accumulation of flavonoid and possibly changes in auxin homeostasis are the underlying mechanism of the observed growth phenotypes and that UVR8 might have an important role for integrating plant growth and stress signals.     

Isolation and characterization of a sterile-dwarf mutant in Asian cotton （Gossypium arboreum L.）

Plant height is an important trait in cotton. To elucidate the molecular mechanisms of the dwarf phenotype, a sterile-dwarf mutant derived from Gossypium arboreum L. cv. Jinhuazhongmian was developed by ^60Co y-ray irradiation. The results demonstrated that the steriledwarf mutant phenotype was controlled by a pair of recessive gene, which was designated sd^a. Plants carrying the sd^a gene contained lower levels of indole-3-acetic acid （IAA） and abscisic acid （ABA） compared with wild-type （WT） plants. The chlorophyll content and net photosynthetic rate in mutant leaves were markedly decreased. However, it was possible that ABA biosynthesis or signaling was involved in governing the sd^a phenotype. Semi-quantitative RT-PCR analysis detected 13 differentially expressed ESTs, and the steriledwarf mutant exhibited decreased expression levels relative to the WT. The role of nine potential hormone biosynthetic genes in the synthesis of IAA, ABA, polyamines （PAs） and jasmonic acid （JA） were discussed.