The genes ABI1 and ABI2 are involved in abscisic acid- and drought-inducible expression of the Daucus carota L. Dc3 promoter in guard cells of transgenic Arabidopsis thaliana (L.) Heynh.

 The ABA INSENSITIVE1 (ABI1) and ABI2 genes encode homologous type-2C protein phosphatases with redundant yet distinct functions in abscisic acid (ABA) responses. Results from Northern blot analysis showed that ABA- and mannitol-inducible expression of the COR47 and COR78/LTI78/RD29A (COR78) genes was more impaired in the abi2 mutant of Arabidopsis thaliana (L.) Heynh than in the abi1 mutant. Furthermore, ABA-plus-mannitol treatments were additive towards COR47 gene expression; however, the ABA-deficient aba1 mutant showed reduced COR expression relative to the wild type in response to mannitol and ABA-plus-mannitol treatments. These results support the notion that drought- and ABA-signalling pathways are separate yet overlapping. To facilitate quantitative analysis of the genetic control of tissue-specific ABA- and desiccation-response pathways, we analyzed ABA- and mannitol-inducible expression of a carrot (Daucus carota L.) Dc3 promoter:uidA (β-glucuronidase; GUS) chimaeric reporter (Dc3-GUS) in transgenic wild-type, ABA-deficient aba1, and ABA-insensitive abi1 and abi2 mutants. The Dc3 promoter directed ABA- and mannitol-inducible GUS expression in Arabidopsis guard cells and the two treatments were additive. The aba1, abi1, and abi2 mutant genotypes had reduced GUS expression in guard cells of cotyledons in response to mannitol, whereas abi1 and abi2 mutants were reduced in ABA-inducible GUS expression, consistent with overlapping ABA- and drought-response pathways. Quantitative fluorometric GUS assays of leaf extracts showed that abi2 mutants responded less to exogenous ABA than did abi1 mutants, and abi2 mutants responded more to mannitol than did abi1 mutants. We conclude that Dc3-GUSArabidopsis is a tractable system in which to study tissue-specific ABA and drought signalling and suggest that ABI2 functions predominantly over ABI1 in COR78 and COR47 gene expression and guard-cell Dc3-GUS expression. Received: 23 May 1999 / Accepted: 3 December 1999     

Crosstalk between ABA and auxin signaling pathways in roots of <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> (L.) Heynh.

Studies of abscisic acid (ABA) and auxin have revealed that these pathways impinge on each other. The Daucus carota (L.) Dc3 promoter: uidA (-glucuronidase: GUS) chimaeric reporter (ProDc3:GUS) is induced by ABA, osmoticum, and the auxin indole-3-acetic acid (IAA) in vegetative tissues of transgenic Arabidopsis thaliana (L.) Heynh. Here, we describe the root tissue-specific expression of ProDc3:GUS in the ABA-insensitive-2 (abi2-1), auxin-insensitive-1 (aux1), auxin-resistant-4 (axr4), and rooty (rty1) mutants of Arabidopsis in response to ABA, IAA and synthetic auxins naphthalene acetic acid (NAA), and 2, 4-(dichlorophenoxy) acetic acid. Quantitative analysis of ProDc3:GUS expression showed that the abi2-1 mutant had reduced GUS activity in response to ABA, IAA, or 2, 4-d, but not to NAA. Similarly, chromogenic staining of ProDc3:GUS activity showed that the aux1 and axr4 mutants gave predictable hypomorphic ProDc3:GUS expression phenotypes in roots treated with IAA or 2, 4-d, but not the diffusible auxin NAA. Likewise the rty mutant, which accumulates auxin, showed elevated ProDc3:GUS expression in the absence or presence of hormones relative to wild type. Interestingly, the aux1 and axr4 mutants showed a hypomorphic effect on ABA-inducible ProDc3:GUS expression, demonstrating that ABA and IAA signaling pathways interact in roots. Possible mechanisms of crosstalk between ABA and auxin signaling are discussed.     

Three Classes of Abscisic Acid (ABA)-Insensitive Mutations of Arabidopsis Define Genes that Control Overlapping Subsets of ABA Responses

Wild type and three abscisic acid (ABA)-insensitive mutants of Arabidopsis (ABI1, ABI2, and ABI3) were compared for their ability to respond to ABA for a variety of ABA-inducible responses throughout the life cycle of the plants. The responses tested included effects on seedling growth, proline accumulation in seedlings, ABA-regulated protein synthesis in plantlets, and seed storage protein and lipid synthesis and accumulation. The abi1 and abi2 mutants showed reduced sensitivity to ABA for inhibition of seedling growth, induction of proline accumulation, and alterations in protein synthesis patterns during vegetative growth, but had wild type levels of storage reserves. In contrast, the abi3 mutant had wild type sensitivity for induction of proline accumulation and was only slightly less responsive to ABA with respect to effects on seedling growth and changes in patterns of protein synthesis. The major effects of this mutation were on seed development. Seeds of the abi3 mutant had two-thirds of the wild type level of storage protein and one-third the wild type level of eicosenoic acid, the major fatty acid component of storage lipids in wild type seeds. These results show that none of the abi mutants is insensitive for all ABA-inducible responses and that the abi3 effects are not seed-specific. Comparison of the degree of ABA sensitivity of monogenic mutant lines with that of digenic mutant lines carrying pairwise combinations of the abi mutations suggests that ABA responses in mature seeds are controlled by at least two parallel pathways.     

A role for arabinogalactan-proteins in root epidermal cell expansion

Arabinogalactan-proteins (AGPs) are abundant plant proteoglycans that react with (β-d-Glc)₃ but not (β-d-Man)₃ Yariv reagent. We report here that treatment with (β-d-Glc)₃ Yariv reagent caused inhibition of root growth of Arabidopsis thaliana (L.) Heynh. seedlings. Moreover, the treated roots exhibited numerous bulging epidermal cells. Treatment with (β-d-Man)₃ Yariv reagent did not have any such effects. These results indicate a role for AGPs in root growth and control of epidermal cell expansion. Because treatment with (β-d-Glc)₃ Yariv reagent phenocopies the reb1 (root epidermal cell bulging) mutant of Arabidopsis, AGPs were extracted from the reb1-1 mutant and compared with those of the wild type. The reb1-1 roots contained an approximately 30% lower level of AGPs than the wild type. More importantly, while the profile of AGPs from wild-type roots showed two major peaks upon crossed electrophoresis, the profile of AGPs from reb1-1 roots exhibited only one of the major peaks. Therefore, the reb1 phenotype appears to be a result of defective or missing root AGPs. Taken together, this pharmacological and genetic evidence strongly indicates a function of AGPs in the control of root epidermal cell expansion. Received: 13 February 1997 / Accepted: 1 April 1997     

Characterization of the growth and auxin physiology of roots of the tomato mutant,diageotropica

Roots of the tomato (Lycopersicon esculentum, Mill.) mutant diageotropica (dgt) exhibit an altered phenotype. These roots are agravitropic and lack lateral roots. Relative to wild-type (VFN8) roots, dgt roots are less sensitive to growth inhibition by exogenously applied IAA and auxin transport inhibitors (phytotropins), and the roots exhibit a reduction in maximal growth inhibition in response to ethylene. However, IAA transport through roots, binding of the phytotropin, tritiated naphthylphthalamic acid ([³H]NPA), to root microsomal membranes, NPA-sensitive IAA uptake by root segments, and uptake of [³H]NPA into root segments are all similar in mutant and wild-type roots. We speculate that the reduced sensitivity of dgt root growth to auxin-transport inhibitors and ethylene is an indirect result of the reduction in sensitivity to auxin in this single gene, recessive mutant. We conclude that dgt roots, like dgt shoots, exhibit abnormalities indicating they have a defect associated with or affecting a primary site of auxin perception or action.Abbreviations BCA bicinchoninic acid - IAA indole 3-acetic acid - dgt diageotropica - IC₅₀ concentration for 50% inhibition of growth - NPA N-1-naphthylphthalamic acid - SCB-1 semicarbazone 1 This research was supported by grants from Sandoz Agro, Inc. (G.K.M), the National Aeronautics and Space Administration (NASA) and the National Science Foundation (T.L.L), and NASA (D.L.R.).     

A multidrug and toxic compound extrusion (MATE) transporter modulates auxin levels in root to regulate root development and promotes aluminium tolerance

MATE (multidrug and toxic compound extrusion) transporters play multiple roles in plants including detoxification, secondary metabolite transport, aluminium (Al) tolerance, and disease resistance. Here we identify and characterize the role of the Arabidopsis MATE transporter DETOXIFICATION30. AtDTX30 regulates auxin homeostasis in Arabidopsis roots to modulate root development and Al-tolerance. DTX30 is primarily expressed in roots and localizes to the plasma membrane of root epidermal cells including root hairs. dtx30 mutants exhibit reduced elongation of the primary root, root hairs, and lateral roots. The mutant seedlings accumulate more auxin in their root tips indicating role of DTX30 in maintaining auxin homeostasis in the root. Al induces DTX30 expression and promotes its localization to the distal transition zone. dtx30 seedlings accumulate more Al in their roots but are hyposensitive to Al-mediated rhizotoxicity perhaps due to saturation in root growth inhibition. Increase in expression of ethylene and auxin biosynthesis genes in presence of Al is absent in dtx30. The mutants exude less citrate under Al conditions, which might be due to misregulation of AtSTOP1 and the citrate transporter AtMATE. In conclusion, DTX30 modulates auxin levels in root to regulate root development and in the presence of Al indirectly modulates citrate exudation to promote Al tolerance.     

Analyses of mutants of three genes that influence root hair development in Zea mays (Gramineae) suggest that root hairs are dispensable

Root hairs are specialized epidermal cells that are thought to play an important role in plant nutrition by facilitating the absorption of water and nutrients. Three maize mutants with abnormal root hair morphologies (rthl, rth2, and rth3) have been isolated from Mutator transposon stocks. All three root hair mutant phenotypes are controlled by single recessive alleles. The rthl mutant initiates normal-looking root hair primordia that fail to elongate. The normal-looking root hair primordia of the rth2 mutant elongate to only approximately one-fifth to one-fourth the length of wild type root hairs. Like rth1 primordia, rth3 primordia undergo little elongation. However, unlike the relatively normal-looking rth1 primordia, rth3 primordia are distinctly abnormal when viewed through a scanning electron microscope. The rth1 mutant exhibits pleiotropic nutrient deficiencies, while the rth2 and rth3 mutants grow vigorously. This finding suggests that under some environmental conditions, root hairs are less important to plant growth than has been previously thought. The rthl, rth2, and rth3 genes have been mapped to chromosomes 1L, 5L, and 1S, respectively, via crosses with BA translocation stocks. The rth2 allele exhibits reduced transmission through the male gametophyte, but a normal rate of transmission through female gametophytes; rth1 and rth3 are transmitted at normal rates.     

Differential Hypocotyl and Root Development of Arabidopsis Auxin-Insensitive Mutants

Arabidopsis , aux1-7, axr1-3 and axr2-1, grown in a natural sandy soil, without sucrose supplementation. The three mutants showed impaired epidermal cell elongation in the hypocotyls of 15-day-old seedlings, with axr2-1 showing the most marked effects. In addition, the roots of axr2-1 elongated faster and presented a more extended meristematic zone than the other genotypes. Unchanged epidermal cell length in the differentiation zone of axr2-1 relative to the wild-type suggested enhancement of cell proliferation. These alterations may have affected the timing and site of emergence of the root hairs, starting later and further from the root tip than in the other genotypes. Similarly to the wild-type, no root hair growth was initiated in axr2-1 drought-induced short roots, although the epidermis was differentiated into trichoblasts and atrichoblasts. On rehydration of the short roots, hair formation occurred from trichoblasts prior to epidermal cell elongation. Therefore, auxin-insensitivity in the axr2-1 mutant did not result in alterations of the hair-forming process itself. The differential development of axr2-1 seedlings, relative to the other auxin-insensitive mutants, suggested that the AXR2 gene has a complex, regulatory function in multiple hormone signaling. Received 26 July 2000/ Accepted in revised form 28 February 2001     

Formin homology 1 (OsFH1) regulates root-hair elongation in rice (Oryza sativa)

The outgrowth of root hairs from the epidermal cell layer is regulated by a strict genetic regulatory system and external growth conditions. Rice plants cultivated in water-logged paddy land are exposed to a soil ecology that differs from the environment surrounding upland plants, such as Arabidopsis and maize. To identify genes that play important roles in root-hair growth, a forward genetics approach was used to screen for short-root-hair mutants. A short-root-hair mutant was identified, and the gene was isolated using map-based cloning and sequencing. The mutant harbored a point mutation at a splicing acceptor site, which led to truncation of OsFH1 (rice formin homology 1). Subsequent analysis of two additional T-DNA mutants verified that OsFH1 is important for root-hair elongation. Further studies revealed that the action of OsFH1 on root-hair growth is dependent on growth conditions. The mutant Osfh1 exhibited root-hair defects when roots were grown submerged in solution, and mutant roots produced normal root hairs in the air. However, root-hair phenotypes of mutants were not influenced by the external supply of hormones or carbohydrates, a deficiency of nutrients, such as Fe or P _i , or aeration. This study shows that OsFH1 plays a significant role in root-hair elongation in a growth condition-dependent manner.     

Serotonin modulates Arabidopsis root growth via changes in reactive oxygen species and jasmonic acid–ethylene signaling

Serotonin (5‐hydroxytryptamine) is a bioactive indoleamine with neurotransmitter function in vertebrates, which represents an emerging signaling molecule in plants, playing key roles in the development and defense. In this study, the role of reactive oxygen species (ROS) and jasmonic acid (JA)–ethylene (Et) signaling in root developmental alterations induced by serotonin was investigated. An Arabidopsis thaliana mutant defective at the RADICAL‐INDUCED CELL DEATH1 (RCD1) locus was resistant to paraquat‐induced ROS accumulation in primary roots and showed decreased inhibition or root growth in response to serotonin. A suite of JA‐ and Et‐related mutants including coronatine insensitive1, jasmonic acid resistant1 (jar1), etr1, ein2 and ein3 showed tolerance to serotonin in the inhibition of primary root growth and ROS redistribution within the root tip when compared with wild‐type (WT) seedlings. Competence assays between serotonin and AgNO₃, a well‐known blocker of Et action, showed that primary root growth in medium supplemented with serotonin was normalized by AgNO_3, whereas roots of eto3, an Et overproducer mutant, were oversensitive to serotonin. Comparison of ROS levels in WT, etr1, jar1 and rcd1 primary root tips using the ROS‐specific probe 2′,7′‐dichlorofluorescein diacetate and confocal imaging showed that serotonin inhibition of primary root growth likely occurs independently of its conversion into melatonin. Our results provide compelling evidence that serotonin affects ROS distribution in roots, involving RCD1 and components of the JA–Et signaling pathways.     

Identification of mutants in phosphorus metabolism

Phosphorus availability is often limiting for plant growth. However, little is known of the pathways and mechanisms that regulate phosphorus (P) uptake and distribution in plants. We have developed a screen based on the induction of secreted root acid phosphatase activity by low‐P stress to identify mutants of Arabidopsis thaliana with defects in P metabolism. Acid phosphatase activity was detected visually in the roots of A. thaliana seedlings grown in vitro on low‐P medium, using the chromogenic substrate, 5‐bromo‐4‐chloro‐3‐indolyl‐phosphate (BCIP). In low‐P stress conditions the roots of wild‐type plants stained blue, as the induced root acid phosphatase cleaved BCIP to release the coloured product. Potential mutants were identified as having white, or pale blue, roots under these conditions. Out of approximately 79 000 T‐DNA mutagenised seedlings screened, two mutants with reduced acid phosphatase staining were further characterised. Both exhibited reduced growth and differences in their P contents when compared to wild‐type A. thaliana. The mutant with the most severe phenotype, pho3, accumulated high levels of anthocyanins and starch in a distinctive visual pattern within the leaves. The phenotypes of these mutants are distinct from two previously identified phosphorus mutants (phol and pho2) and from an acid phosphatase deficient mutant (pupl) of A. thaliana. This suggested that the screening method was robust and might lead to the identification of further mutants with the potential for increasing our understanding of P nutrition.     

The responses of wild-type and ABA mutant Arabidopsis thaliana plants to phosphorus starvation

The growth patterns of plants subjected to phosphorus starvation resemble those caused by treatment with ABA, suggesting that ABA could mediate the response of the plant to phosphorus starvation. We examined the role of ABA in phosphorus stress by comparing growth and biochemical responses of Arabidopsis thaliana ABA mutants aba-1 and abi2-1 to those of wild-type plants. We first characterized acid phosphatase production of wild-type Arabidopsis in response to phosphorus starvation. We found that several acid phosphatase isozymes are present in roots and shoots, but only a subset of these isozymes are induced by phosphorus stress, and they are induced in both organs. Production of acid phosphatase in response to phosphorus stress was not affected by the aba-1 or abi2-1 mutations. Low phosphorus also resulted in decreased growth of both wild-type and ABA mutant plants, and the root-to-shoot ratio was increased in both wild type and mutants. Anthocyanins accumulated in response to phosphorus stress in both wild-type and mutant plants, but the increase was reduced in the aba-1 mutant. Thus, two different ABA mutants responded normally in most respects to phosphorus stress. Our data do not support a major role for ABA in coordinating the phosphorus-stress response.     

Abscisic acid-insensitive mutations provide evidence for stage-specific signal pathways regulating expression of an Arabidopsis late embryo genesis-abundant (lea) gene

An Arabidopsis homolog of the abscisic acid (ABA)-inducible cotton D19 and wheat Em genes was cloned and its expression assayed at two developmental stages in wild-type, ABA-deficient (aba) and three ABA-insensitive (abi) lines of Arabidopsis thaliana. Expression of this gene was reduced slightly in seeds of aba mutants and approximately ten-fold in abi3 mutants, but seed expression was not decreased in either abi1 or abi2 monogenic mutants. In contrast, the abi1 and abi2 mutants showed a very slight reduction of ABA inducibility in 8-day-old plants, while the responses of aba and abi3 mutants were comparable to that of wild type. Although previous studies have shown that none of the abi mutations show completely stage-specific effects, the results reported here indicate that the importance of each of the ABI loci in regulating this single gene is stage-dependent. Furthermore, the fact that none of the abi mutations show more than minor effects on exogenous ABA inducibility of the Arabidopsis D19/Em homolog in young plants suggests that an additional ABA signalling pathway may be operating during vegetative growth.     

Growth and gibberellin-A1 metabolism in normal and gibberellin-insensitive (Rht3) wheat (Triticum aestivum L.) seedlings

Growth parameters were determined for tall (rht3) and dwarf (Rht3) seedlings of wheat (Triticum aestivum L.). Plant statures and leaf length were reduced by 50% in dwarfs but root and shoot dry weights were less affected. Leaves of dwarf seedlings had shorter epidermal cells and the numbers of cells per rank in talls and dwarfs matched the observed relationships in overall length. Talls grew at twice the rate of dwarfs (2.3 compared with 1.2 mm h^-1). [³H]Gibberellin A₁ ([³H]GA₁) was fed to seedlings via the third leaf and metabolism was followed over 12 h. Immature leaves of tall seedlings transferred radioactivity rapidly to compounds co-chromatographing with [³H]gibberellin A₈ ([³H]GA₈) and a conjugate of [³H]GA₈, whereas leaves of dwarf seedlings metabolised [³H]GA₁ more slowly. Roots of both genotypes produced [³H]GA₈-like material at similar rates. Isotopic dilution studies indicated a reduced 2-hydroxylation capacity in dwarfs, but parallel estimates of the endogenous GA pool size, obtained by radioimmunoassay, indicated a 12–15 times higher level of GA in the dwarf immature leaves. Dwarfing by the Rht3 gene does not appear to operate through enhanced, or abnormal metabolism of active gibberellins and the act of GA metabolism does not bear an obligate relationship to the growth response.Abbreviations GA_n gibberellin A_n - HPLC high-performance liquid chromatography     

Growth and ultrastructure ofArabidopsis root hairs: therhd3 mutation alters vacuole enlargement and tip growth

The root hairs of plants are tubular projections of root epidermal cells and are suitable for investigating the control of cellular morphogenesis. In wild-typeArabidopsis thaliana (L.) Heynh, growing root hairs were found to exhibit cellular expansion limited to the apical end of the cell, a polarized distribution of organelles in the cytoplasm, and vesicles of several types located near the growing tip. Therhd3 mutant produces short and wavy root hairs with an average volume less than one-third of the wild-type hairs, indicating abnormal cell expansion. The mutant hairs display a striking reduction in vacuole size and a corresponding increase in the relative proportion of cytoplasm throughout hair development. Bead-labeling experiments and ultrastructural analyses indicate that the wavy-hair phenotype of the mutant is caused by asymmetric tip growth, possibly due to abnormally distributed vesicles in cortical areas flanking the hair tips. It is suggested that a major effect of therhd3 mutation is to inhibit vacuole enlargement which normally accompanies root hair cell expansion.     

Arabidopsis phosphatidylinositol 4-phosphate 5-kinase genes PIP5K7, PIP5K8, and PIP5K9 are redundantly involved in root growth adaptation to osmotic stress

Phosphatidylinositol 4-phosphate 5-kinase (PIP5K) produces phosphatidylinositol (4,5)-bisphosphate (PtdIns(4,5)P₂), a signaling phospholipid critical for various cellular processes in eukaryotes. The Arabidopsis thaliana genome encodes 11 PIP5K genes. Of these, three type B PIP5K genes, PIP5K7, PIP5K8, and PIP5K9, constitute a subgroup highly conserved in land plants, suggesting that they retain a critical function shared by land plants. In this study, we comprehensively investigated the biological functions of the PIP5K7–9 subgroup genes. Reporter gene analyses revealed their preferential expression in meristematic and vascular tissues. Their YFP-fusion proteins localized primarily to the plasma membrane in root meristem epidermal cells. We selected a mutant line that was considered to be null for each gene. Under normal growth conditions, neither single mutants nor multiple mutants of any combination exhibited noticeable phenotypic changes. However, stress conditions with mannitol or NaCl suppressed main root growth and reduced proximal root meristem size to a greater extent in the pip5k7pip5k8pip5k9 triple mutant than in the wild type. In root meristem epidermal cells of the triple mutant, where plasma membrane localization of the PtdIns(4,5)P₂ marker P24Y is impaired to a large extent, brefeldin A body formation is retarded compared with the wild type under hyperosmotic stress. These results indicate that PIP5K7, PIP5K8, and PIP5K9 are not required under normal growth conditions, but are redundantly involved in root growth adaptation to hyperosmotic conditions, possibly through the PtdIns(4,5)P₂ function promoting plasma membrane recycling in root meristem cells.     

A role for gibberellic acid in orienting microtubules and regulating cell growth polarity in the maize root cortex

The role of gibberellins and cortical microtubules in determining the polarity of cell growth in the root cortex of maize (Zea mays L.) was examined. Inhibition of gibberellin biosynthesis, either naturally through mutation (d5 mutant) or by means of chemicals such as 2S,3S paclobutrazol, caused thickening of root apices and increased their starch content. Immunofluorescence microscopy of cortical microtubules, coupled with a comparison of cell widhts, lengths and shapes, indicated that the meristem and immediate post-mitotic zone were the targets of gibberellin deficiency. Cortical cells in these regions were impaired in their ability to develop highly ordered transversal arrays of cortical microtubules. Consequently, the cells became wider and shorter. Application of gibberellic acid re-established the arrangements of cortical microtubules and the polarity of cell growth characteristic for roots having normal levels of gibberellins, it also decreased the starch content. These results indicate that gibberellins are morphogenetically active substances, not only in shoots but also in roots of maize.Abbreviations CMT cortical microtubule - GA gibberellin - GA₃ gibberellic acid - MT microtubule - PIG postmitotic isodiametric growth The authors acknowledge the support to F.B. from the Royal Society (London UK). We also thank Dr. J. Lenton (University of Bristol, Long Ashton Research Station) who kindly supplied us with 2S,3S paclobutrazol and grains of the GA-deficient d5 mutant of maize.     

Sterilizing Effect of the Mutant Allele sbr 10 (l(1)ts403) in Compound with Null Allele in Drosophila melanogaster Females

In females of Df(1)v-L4/+(0/+) genotype, the presence of the wild-type allele ofsmall bristles (sbr) gene in a single dose has no significant effect on their fecundity, whereas a reduced dose of the temperature-sensitive allele sbr ¹⁰ (l(1)ts403) causes a strong sterilizing effect in females Df(1)v-L4/sbr ¹⁰ (0/sbr ¹⁰) at permissive temperature. We studied the contribution to this effects of the following factors: resorption of egg chambers, decreased oviposition, offspring death at the embryonic and larval stages, and reduced fecundity in females 0/sbr ¹⁰. Sterilizing effect of the mutant sbr ¹⁰ allele proved to be primarily caused by offspring lethality at the embryonic and first-instar larval stages. In 0/+ females, the majority of undeveloped eggs contained embryos that perished at the late developmental stages, whereas in females 0/sbr ¹⁰, at least 50% of undeveloped egg showed no visible signs of development or the embryo development was arrested at early stages of embryogenesis. The results obtained suggest insufficiency of the temperature-sensitive allele sbr ¹⁰ in haploid state to ensure the reproductive functions of Drosophila melanogaster females.     

The maize disorganized aleurone layer 1 and 2 ( dil1, dil2) mutants lack control of the mitotic division plane in the aleurone layer of developing endosperm

The maize (Zea mays L.) endosperm consists of an epidermal like layer of isodiametric aleurone cells surrounding a central body of starchy endosperm cells. In disorgal1 (dil1) and disorgal2 (dil2) mutants the control of the mitotic division plane is relaxed or missing, resulting in mature grains with disorganized aleurone layers. In addition to orientation of the division plane, both the shape and size of the aleurone cells are affected, and often more than one layer of aleurone cells is present. Homozygous dil1 and dil2 grains are shrunken due to reduced accumulation of starchy endosperm and premature developmental arrest of the embryo, and mature mutant grains germinate at a very low rate and fail to develop into plants. However, homozygous mutant plants can be obtained through embryo rescue, revealing that both mutants have an irregular leaf epidermis as well as roots with a strongly reduced number of root hairs and aberrant root hair morphology. Our results suggest the presence of common regulatory mechanisms for the control of cell division orientation in the aleurone and plant epidermis.Abbreviations DAP days after pollination - dek defective kernel mutant - dil disorganized aleurone layer mutant - GUS -glucuronidase - LM light microscopy - PPB pre-prophase band - SEM scanning electron microscopy - TUSC Trait Utility System for Corn     

The Role of ABI3 and FUS3 Loci in Arabidopsis thaliana on Phase Transition from Late Embryo Development to Germination

Arabidopsis abi3 and fus3 mutants are defective in late embryo development and their embryos show precocious growth. To understand the function and role of ABI3 and FUS3, we analyzed expression patterns of genes which were normally activated during late embryo development and germination in these mutants. Using the differential display method, both upregulated and downregulated genes were observed in immature siliques of the abi3 fus3 double mutant. Four clones having more abundant expression in the abi3 fus3 double mutant than in wild type were isolated. These genes were activated during wild-type germination, suggesting that some genes that are activated during wild-type germination are precociously activated in the abi3 fus3 mutant during late embryo development. Also, genes that were activated during wild-type germination were isolated and their expression patterns during late embryo development in the wild type and in abi3, fus3, and abi3 fus3 mutants were analyzed. Sixteen such clones were found, and 11 of these showed derepression or precocious activation of gene expression in the mutants. These results indicate that ABI3 and FUS3 negatively regulate a particular set of genes during late embryo development. We also showed that immature fus3 siliques accumulated one-third of the wild-type level of abscisic acid (ABA), but mature fus3 siliques accumulated ABA at a level comparable to that in the wild type. The possible mechanisms of controlling developmental timing in late embryo development as well as collaborative and distinct roles of ABI3 and FUS3 are discussed.