Search

A description of Arabidopsis DA1, encoding a forecasted ubiquitin receptor, which sets final seed and organ size by limiting the time of cell proliferation, is presented. It is observed that the mutant protein encoded by the da1-1 allele has negative work toward DA1 and a DA1-related (DAR) protein, and overexpression of da1-1 cDNA drastically increases seed and organ size of wild-type plants and recognizes this small gene group as significant regulators of seed and organ size in plants. more...

Sugars not only serve as energy and cellular carbon skeleton but also function as signaling molecules regulating growth and development in plants. Understanding the molecular mechanisms in sugar signaling pathways will provide more information for improving plant growth and development. Here, we describe a sugar-hypersensitive recessive mutant, tang1. Light-grown tang1 mutants have short roots and increased starch and anthocyanin contents when grown on high-sugar concentration medium. Dark-grown tang1 plants exhibit sugar-hypersensitive hypocotyl elongation and enhanced dark development. The tang1 mutants also show an enhanced response to abscisic acid but reduced response to ethylene. Thus, tang1 displays a range of alterations in sugar signaling-related responses. The TANG1 gene was isolated by a map-based cloning approach and encodes a previously uncharacterized unique protein with a predicted Symplekin tight-junction protein C terminus. Expression analysis indicates that TANG1 is ubiquitously expressed at moderate levels in different organs and throughout the Arabidopsis (Arabidopsis thaliana) life cycle; however, its expression is not affected by high-sugar treatment. Genetic analysis shows that PRL1 and TANG1 have additive effects on sugar-related responses. Furthermore, the mutation of TANG1 does not affect the expression of genes involved in known sugar signaling pathways. Taken together, these results suggest that TANG1, a unique gene, plays an important role in sugar responses in Arabidopsis. [ABSTRACT FROM AUTHOR] more...

Organ growth involves the coordination of cell proliferation and cell growth with differentiation. Endoreduplication is correlated with the onset of cell differentiation and with cell and organ size, but little is known about the molecular mechanisms linking cell and organ growth with endoreduplication. We have previously demonstrated that the ubiquitin receptor DA1 influences organ growth by restricting cell proliferation. Here, we show that DA1 and its close family members DAR1 and DAR2 are redundantly required for endoreduplication during leaf development. DA1, DAR1, and DAR2 physically interact with the transcription factors TCP14 and TCP15, which repress endoreduplication by directly regulating the expression of cell-cycle genes. We also show that DA1, DAR1, and DAR2 modulate the stability of TCP14 and TCP15 proteins in Arabidopsis thaliana. Genetic analyses demonstrate that DA1, DAR1, and DAR2 function in a common pathway with TCP14/15 to regulate endoreduplication. Thus, our findings define an important genetic and molecular mechanism involving the ubiquitin receptors DA1, DAR1, and DAR2 and the transcription factors TCP14 and TCP15 that links endoreduplication with cell and organ growth. [ABSTRACT FROM AUTHOR] more...

Seed size in higher plants is determined by the coordinated growth of the embryo, endosperm, and maternal tissue. Several factors that act maternally to regulate seed size have been identified, such as AUXIN RESPONSE FACTOR2, APETALA2, KLUH, and DA1, but the genetic and molecular mechanisms of these factors in seed size control are almost totally unknown. We previously demonstrated that the ubiquitin receptor DA1 acts synergistically with the E3 ubiquitin ligase ENHANCER1 OF DA1 (EOD1)/BIG BROTHER to regulate the final size of seeds in Arabidopsis thaliana. Here, we describe another RING-type protein with E3 ubiquitin ligase activity, encoded by DA2 , which regulates seed size by restricting cell proliferation in the maternal integuments of developing seeds. The da2-1 mutant forms large seeds, while overexpression of DA2 decreases seed size of wild-type plants. Overexpression of rice (Oryza sativa) GRAIN WIDTH AND WEIGHT2 , a homolog of DA2 , restricts seed growth in Arabidopsis. Genetic analyses show that DA2 functions synergistically with DA1 to regulate seed size, but does so independently of EOD1. Further results reveal that DA2 interacts physically with DA1 in vitro and in vivo. Therefore, our findings define the genetic and molecular mechanisms of three ubiquitin-related proteins DA1, DA2, and EOD1 in seed size control and indicate that they are promising targets for crop improvement. [ABSTRACT FROM AUTHOR] more...

The control of organ growth by coordinating cell proliferation and differentiation is a fundamental developmental process. In plants, postembryonic root growth is sustained by the root meristem. For maintenance of root meristem size, the rate of cell differentiation must equal the rate of cell division. Cytokinin and auxin interact to affect the cell proliferation and differentiation balance and thus control root meristem size. However, the genetic and molecular mechanisms that determine root meristem size still remain largely unknown. Here, we report that dal-related protein2 (dar2) mutants produce small root meristems due to decreased cell division and early cell differentiation in the root meristem of Arabidopsis (Arabidopsis thaliana). darl mutants also exhibit reduced stem cell niche activity in the root meristem. DAR2 encodes a Lin-11, Isl-1, and Mec-3 domain-containing protein and shows an expression peak in the border between the transition zone and the elongation zone. Genetic analyses show that DAR2 functions downstream of cytokinin and SHORT HYPOCOTYL2 to maintain normal auxin distribution by influencing auxin transport. Further results indicate that DAR2 acts through the PLETHORA pathway to influence root stem cell niche activity and therefore control root meristem size. Collectively, our findings identify the role of DAR2 in root meristem size control and provide a novel link between several key regulators influencing root meristem size. [ABSTRACT FROM AUTHOR] more...

Guard cell actin reorganization has been observed in stomatal responses to a wide array of stimuli. However, how the guard cell signaling machinery regulates actin dynamics is poorly understood. Here, we report the identification of an allele of the Arabidopsis thaliana ACTIN-RELATED PROTEIN C2 / DISTORTED TRICHOMES2 (ARPC2) locus (encoding the ARPC2 subunit of the ARP2/3 complex) designated high sugar response3 (hsr3). The hsr3 mutant showed increased transpirational water loss that was mainly due to a lesion in stomatal regulation. Stomatal bioassay analyses revealed that guard cell sensitivity to external stimuli, such as abscisic acid (ABA), CaCl2, and light/dark transition, was reduced or abolished in hsr3. Analysis of a nonallelic mutant of the ARP2/3 complex suggested no pleiotropic effect of ARPC2 beyond its function in the complex in regard to stomatal regulation. When treated with ABA , guard cell actin filaments underwent fast disruption in wild-type plants, whereas those in hsr3 remained largely bundled. The ABA insensitivity phenotype of hsr3 was rescued by cytochalasin D treatment, suggesting that the aberrant stomatal response was a consequence of bundled actin filaments. Our work indicates that regulation of actin reassembly through ARP2/3 complex activity is crucial for stomatal regulation. [ABSTRACT FROM AUTHOR] more...

The actin cytoskeleton mediates cellular processes through the dynamic regulation of the time, location, and extent of actin polymerization. Actin polymerization is controlled by several types of evolutionarily conserved proteins, including those comprising the ARP2/3 complex. In animal cells ARP2/3 activity is regulated by WAVE complexes that contain WAVE/SCAR proteins, PIR121, Nap 125, and other proteins. The activity of the WAVE complex is regulated by Rho-GTPase-mediated signaling that leads to ARP2/3 activation by WAVE/SCAR proteins. We describe in this report Arabidopsis (Arabidopsis thaliana) genes encoding Nap and PIR proteins. Light-grown Atnap-1 and Atpir-1 mutant plants displayed altered leaf, inflorescence, silique, and seed set phenotypes. Dark-grown Atnap-T! and Atpir-1 seedlings also exhibited longer roots, enhanced skotomorphogenesis and Glc responses, and shorter thicker hypocotyls than those of wild type, showing that A/NAP and AtPIR participate in a variety of growth and developmental processes. Mutations in AtNAP and AtPIR caused cell morphology defects in cotyledon pavement cells and trichomes seen in mutants in ARP2/3 subunits and in plants expressing constitutively active Rop2 GTPase. The patterns and levels of actin polymerization observed in Atnap-1 and Atpir-1 mutant trichome cells and epidermal pavement cell morphology is consistent with Arabidopsis NAP and PIR proteins forming a WAVE complex that activates ARP2/3 activity. The multiple growth and developmental phenotypes of Atnap and Atpir mutants reveals these proteins are also required for a wider variety of cellular functions in addition to regulating trichome cell growth. [ABSTRACT FROM AUTHOR] more...