Defective pollen wall is required for anther and microspore development in rice and encodes a fatty acyl carrier protein reductase

Aliphatic alcohols naturally exist in many organisms as important cellular components; however, their roles in extracellular polymer biosynthesis are poorly defined. We report here the isolation and characterization of a rice (Oryza sativa) male-sterile mutant, defective pollen wall (dpw), which displays defective anther development and degenerated pollen grains with an irregular exine. Chemical analysis revealed that dpw anthers had a dramatic reduction in cutin monomers and an altered composition of cuticular wax, as well as soluble fatty acids and alcohols. Using map-based cloning, we identified the DPW gene, which is expressed in both tapetal cells and microspores during anther development. Biochemical analysis of the recombinant DPW enzyme shows that it is a novel fatty acid reductase that produces 1-hexadecanol and exhibits >270-fold higher specificity for palmiltoyl-acyl carrier protein than for C16:0 CoA substrates. DPW was predominantly targeted to plastids mediated by its N-terminal transit peptide. Moreover, we demonstrate that the monocot DPW from rice complements the dicot Arabidopsis thaliana male sterile2 (ms2) mutant and is the probable ortholog of MS2. These data suggest that DPWs participate in a conserved step in primary fatty alcohol synthesis for anther cuticle and pollen sporopollenin biosynthesis in monocots and dicots.     

AtNG1 encodes a protein that is required for seed germination

The pentatricopeptide repeat (PPR) family of eukaryotic proteins has numerous members in plants and is important for plant development. In the present study, we cloned a novel PPR gene, designated AtNG1, and characterized the ng1 Arabidopsis mutant. Morphological and structural observation of an ng1 mutant revealed that its sexual reproduction and seed formation processes are essentially normal. The mature embryonic root of ng1 is fully developed and has a well-differentiated structure; however, ng1 seeds cannot germinate, even when supplied with supplemental hormones and nutrition. Further investigation showed that embryo expansion and root cell elongation fails to occur after water imbibitions. Transient gene expression analysis indicated that AtNG1 localizes in mitochondrion. This implies that the deficiency of mitochondrion function might be the reason for the failed seed germination. Thus, our finding confirmed that AtNG1 plays a critical role in the early process of seed germination.     

The indeterminate gametophyte1 gene of maize encodes a LOB domain protein required for embryo Sac and leaf development

Angiosperm embryo sac development begins with a phase of free nuclear division followed by cellularization and differentiation of cell types. The indeterminate gametophyte1 (ig1) gene of maize (Zea mays) restricts the proliferative phase of female gametophyte development. ig1 mutant female gametophytes have a prolonged phase of free nuclear divisions leading to a variety of embryo sac abnormalities, including extra egg cells, extra polar nuclei, and extra synergids. Positional cloning of ig1 was performed based on the genome sequence of the orthologous region in rice. ig1 encodes a LATERAL ORGAN BOUNDARIES domain protein with high similarity to ASYMMETRIC LEAVES2 of Arabidopsis thaliana. A second mutant allele of ig1 was identified in a noncomplementation screen using active Mutator transposable element lines. Homozygous ig1 mutants have abnormal leaf morphology as well as abnormal embryo sac development. Affected leaves have disrupted abaxial-adaxial polarity and fail to repress the expression of meristem-specific knotted-like homeobox (knox) genes in leaf primordia, causing a proliferative, stem cell identity to persist in these cells. Despite the superficial similarity of ig1-O leaves and embryo sacs, ectopic knox gene expression cannot be detected in ig1-O embryo sacs.     

vanishing tassel2 encodes a grass-specific tryptophan aminotransferase required for vegetative and reproductive development in maize

Auxin plays a fundamental role in organogenesis in plants. Multiple pathways for auxin biosynthesis have been proposed, but none of the predicted pathways are completely understood. Here, we report the positional cloning and characterization of the vanishing tassel2 (vt2) gene of maize (Zea mays). Phylogenetic analyses indicate that vt2 is a co-ortholog of TRYPTOPHAN AMINOTRANSFERASE OF ARABIDOPSIS1 (TAA1), which converts Trp to indole-3-pyruvic acid in one of four hypothesized Trp-dependent auxin biosynthesis pathways. Unlike single mutations in TAA1, which cause subtle morphological phenotypes in Arabidopsis thaliana, vt2 mutants have dramatic effects on vegetative and reproductive development. vt2 mutants share many similarities with sparse inflorescence1 (spi1) mutants in maize. spi1 is proposed to encode an enzyme in the tryptamine pathway for Trp-dependent auxin biosynthesis, although this biochemical activity has recently been questioned. Surprisingly, spi1 vt2 double mutants had only a slightly more severe phenotype than vt2 single mutants. Furthermore, both spi1 and vt2 single mutants exhibited a reduction in free auxin levels, but the spi1 vt2 double mutants did not have a further reduction compared with vt2 single mutants. Therefore, both spi1 and vt2 function in auxin biosynthesis in maize, possibly in the same pathway rather than independently as previously proposed.     

The arabidopsis serrate gene encodes a zinc-finger protein required for normal shoot development

Organogenesis in plants depends upon the proper regulation of many genes, but how such necessary changes in gene expression are coordinated is largely unknown. The serrate (se) mutant of Arabidopsis displays defects in the initiation and elaboration of cotyledons and post-embryonic lateral organs. Cloning the SE gene revealed that it encodes a protein with a single, C(2)H(2)-type, zinc finger related to genes in other eukaryotes. Consistent with a role in organogenesis, the SE gene is transcribed in shoot meristems and in emerging organ primordia throughout development. Expression of the SE cDNA under the control of a heterologous promoter caused both accelerated and arrested plant growth, and these phenotypes were due to overexpression and co-suppression of the SE gene, respectively. Our analysis of the se mutant and the SE gene suggests a role for the SE gene product in regulating changes in gene expression via chromatin modification. Consistent with this proposed function, a synergistic double mutant phenotype was seen for plants mutant at both the SE locus and the locus encoding the largest subunit of chromatin assembly factor I.     

TANMEI/EMB2757 encodes a WD repeat protein required for embryo development in Arabidopsis

We identified the Arabidopsis (Arabidopsis thaliana) tanmei/emb2757 (tan) mutation that causes defects in both embryo and seedling development. tan mutant embryos share many characteristics with the leafy cotyledon (lec) class of mutants in that they accumulate anthocyanin, are intolerant of desiccation, form trichomes on cotyledons, and have reduced accumulation of storage proteins and lipids. Thus, TAN functions both in the early and late phases of embryo development. Moreover, the TAN and LEC genes interact synergistically, suggesting that they do not act in series in the same genetic pathway but, rather, that they have overlapping roles during embryogenesis. tan mutants die as embryos, but immature mutant seeds can be germinated in culture. However, tan mutant seedlings are defective in shoot and root development, their hypocotyls fail to elongate in the dark, and they die as seedlings. We isolated the TAN gene and showed that the predicted polypeptide has seven WD repeat motifs, suggesting that TAN forms complexes with other proteins. Together, these results suggest that TAN interacts with other proteins to control many aspects of embryo development.     

Young Seedling Stripe1 encodes a chloroplast nucleoid-associated protein required for chloroplast development in rice seedlings

Planta - Young Seedling Stripe1 (YSS1) was characterized as an important regulator of plastid-encoded plastid RNA polymerase (PEP) activity essential for chloroplast development at rice seedling...     

The TORMOZ gene encodes a nucleolar protein required for regulated division planes and embryo development in Arabidopsis

Embryogenesis in Arabidopsis thaliana is marked by a predictable sequence of oriented cell divisions, which precede cell fate determination. We show that mutation of the TORMOZ (TOZ) gene yields embryos with aberrant cell division planes and arrested embryos that appear not to have established normal patterning. The defects in toz mutants differ from previously described mutations that affect embryonic cell division patterns. Longitudinal division planes of the proembryo are frequently replaced by transverse divisions and less frequently by oblique divisions, while divisions of the suspensor cells, which divide only transversely, appear generally unaffected. Expression patterns of selected embryo patterning genes are altered in the mutant embryos, implying that the positional cues required for their proper expression are perturbed by the misoriented divisions. The TOZ gene encodes a nucleolar protein containing WD repeats. Putative TOZ orthologs exist in other eukaryotes including Saccharomyces cerevisiae, where the protein is predicted to function in 18S rRNA biogenesis. We find that disruption of the Sp TOZ gene results in cell division defects in Schizosaccharomyces pombe. Previous studies in yeast and animal cells have identified nucleolar proteins that regulate the exit from M phase and cytokinesis, including factors involved in pre-rRNA processing. Our study suggests that in plant cells, nucleolar functions might interact with the processes of regulated cell divisions and influence the selection of longitudinal division planes during embryogenesis.     

l7Rn6 encodes a novel protein required for clara cell function in mouse lung development

The highly secretory Clara cells play a pivotal role in protecting the lung against inflammation and oxidative stress. This study reports the positional cloning of a novel protein required for Clara cell physiology in mouse lung development. The perinatal lethal N-ethyl-N-nitrosourea-induced l7Rn6(4234SB) allele contained a nonsense mutation in the previously hypothetical gene NM_026304 on chromosome 7. Whereas l7Rn6 mRNA levels were indistinguishable from wild type, l7Rn6(4234SB) homozygotes exhibited decreased expression of the truncated protein, suggesting protein instability. During late gestation, l7Rn6 was widely expressed in the cytoplasm of lung epithelial cells, whereas perinatal expression was restricted to the bronchiolar epithelium. Homozygosity for the l7Rn6(4234SB) allele did not affect early steps in lung patterning, growth, or cellular differentiation. Rather, mutant lungs demonstrated severe emphysematous enlargement of the distal respiratory sacs at birth. Clara cell pathophysiology was evident from decreased cytoplasmic CCSP and SP-B protein levels, enlargement and disorganization of the Golgi complex, and formation of aberrant vesicular structures. Additional support for a role in the secretory pathway derived from l7Rn6 localization to the endoplasmic reticulum. Thus, l7Rn6 represents a novel protein required for organization and/or function of the secretory apparatus in Clara cells in mouse lung.     

SIMPLE LEAF3 encodes a ribosome‐associated protein required for leaflet development in Cardamine hirsuta

Leaves show considerable variation in shape, and may be described as simple, when the leaf is entire, or dissected, when the leaf is divided into individual leaflets. Here, we report that the SIMPLE LEAF3 (SIL3) gene is a novel determinant of leaf shape in Cardamine hirsuta – a dissected‐leaved relative of the simple‐leaved model species Arabidopsis thaliana. We show that SIL3 is required for leaf growth and leaflet formation but leaf initiation is less sensitive to perturbation of SIL3 activity. SIL3 is further required for KNOX (knotted1‐like homeobox) gene expression and localized auxin activity maxima, both of which are known to promote leaflet formation. We cloned SIL3 and showed that it encodes RLI2 (RNase L inhibitor 2), an ATP binding cassette‐type ATPase with important roles in ribosome recycling and translation termination that are conserved in eukaryotes and archaea. RLI mutants have not been described in plants to date, and this paper highlights the potential of genetic studies in C. hirsuta to uncover novel gene functions. Our data indicate that leaflet development is sensitive to perturbation of RLI2‐dependent aspects of cellular growth, and link ribosome function with dissected‐leaf development.     

The Myxococcus xanthus asgA gene encodes a novel signal transduction protein required for multicellular development.

The Myxococcus xanthus asgA gene is one of three known genes necessary for the production of extracellular A-signal, a cell density signal required early in fruiting body development. We determined the DNA sequence of asgA. The deduced 385-amino-acid sequence of AsgA was found to contain two domains: one homologous to the receiver domain of response regulators and the other homologous to the transmitter domain of histidine protein kinases. A kanamycin resistance (Kmr) gene was inserted at various positions within or near the asgA gene to determine the null phenotype. Those strains with the Kmr gene inserted upstream or downstream of asgA are able to form fruiting bodies, while strains containing the Kmr gene inserted within asgA fail to develop. The nature and location of the asgA476 mutation were determined. This mutation causes a leucine-to-proline substitution within a conserved stretch of hydrophobic residues in the N-terminal receiver domain. Cells containing the insertion within asgA and cells containing the asgA476 substitution have similar phenotypes with respect to development, colony color, and expression of an asg-dependent gene. An analysis of expression of a translational asgA-lacZ fusion confirms that asgA is expressed during growth and early development. Finally, we propose that AsgA functions within a signal transduction pathway that is required to sense starvation and to respond with the production of extracellular A-signal.