<Emphasis Type="Italic">odd-skipped</Emphasis> homologs function during gut development in<Emphasis Type="Italic"> C. elegans</Emphasis>

Genes in the odd-skipped (odd) family encode a discrete subset of C2H2 zinc finger proteins that are widely distributed among metazoan phyla. Although the initial member (odd) was identified as a Drosophila pair-rule gene, various homologs are expressed within each of the three germ layers in complex patterns that suggest roles in many pathways beyond segmentation. To further investigate the evolutionary history and extant functions of genes in this family, we have initiated a characterization of two homologs, odd-1 and odd-2, identified in the genome of the nematode, Caenorhabditis elegans. Sequence comparisons with homologs from insects (Drosophila and Anopheles) and mammals suggest that two paralogs were present within an ancestral metazoan; additional insect paralogs and both extant mammalian genes likely resulted from gene duplications that occurred after the split between the arthropods and chordates. Analyses of gene function using RNAi indicate that odd-1 and odd-2 play essential and distinct roles during gut development. Specific expression of both genes in the developing intestine and other cells in the vicinity of the gut was shown using GFP-reporters. These results indicate primary functions for both genes that are most like those of the Drosophila paralogs bowel and drumstick, and support a model in which gut specification represents the ancestral role for genes in this family.Edited by C. Desplan     

Functional divergence of <Emphasis Type="Italic">GhCFE5</Emphasis> homoeologs revealed in cotton fiber and <Emphasis Type="Italic">Arabidopsis</Emphasis> root cell development

Key message

In GhCFE5 homoeologs, GhCFE5D interacted with more actin homologs and stronger interaction activity than GhCFE5A. GhCFE5D - but not GhCFE5A -overexpression severely disrupted actin cytoskeleton organization and significantly suppressed cell elongation.

Abstract

Homoeologous genes are common in polyploid plants; however, their functional divergence is poorly elucidated. Allotetraploid Upland cotton (Gossypium hirsutum, AADD) is the most widely cultivated cotton; accounting for more than 90 % of the world’s cotton production. Here, we characterized GhCFE5A and GhCFE5D homoeologs from G. hirsutum acc TM-1. GhCFE5 homoeologs are expressed preferentially in fiber cells; and a significantly greater accumulation of GhCFE5A mRNA than GhCFE5D mRNA was found in all tested tissues. Overexpression of GhCFE5D but not GhCFE5A seriously inhibits the Arabidopsis hypocotyl and root cell elongation. Yeast two-hybrid assay and bimolecular fluorescence complementation (BiFC) analysis showed that compared with GhCFE5A, GhCFE5D interacts with more actin homologs and has a stronger interaction activity both from Arabidopsis and Upland cotton. Interestingly, subcellular localization showed that GhCFE5 resides on the cortical endoplasmic reticulum (ER) network and is colocalized with actin cables. The interaction activities between GhCFE5 homoeologs and actin differ in their effects on F-actin structure in transgenic Arabidopsis root cells. The F-actin changed direction from vertical to lateral, and the actin cytoskeleton organization was severely disrupted in GhCFE5D-overexpressing root cells. These data support the functional divergence of GhCFE5 homoeologs in the actin cytoskeleton structure and cell elongation, implying an important role for GhCFE5 in the evolution and selection of cotton fiber.

     

Molecular characterization the <Emphasis Type="Italic">YABBY</Emphasis> gene family in <Emphasis Type="Italic">Oryza sativa</Emphasis> and expression analysis of <Emphasis Type="Italic">OsYABBY1</Emphasis>

Members of the YABBY gene family have a general role that promotes abaxial cell fate in a model eudicot, Arabidopsis thaliana. To understand the function of YABBY genes in monocots, we have isolated all YABBY genes in Oryza sativa (rice), and revealed the spatial and temporal expression pattern of one of these genes, OsYABBY1. In rice, eight YABBY genes constitute a small gene family and are classified into four groups according to sequence similarity, exon-intron structure, and organ-specific expression patterns. OsYABBY1 shows unique spatial expression patterns that have not previously been reported for other YABBY genes, so far. OsYABBY1 is expressed in putative precursor cells of both the mestome sheath in the large vascular bundle and the abaxial sclerenchyma in the leaves. In the flower, OsYABBY1 is specifically expressed in the palea and lemma from their inception, and is confined to several cell layers of these organs in the later developmental stages. The OsYABBY1-expressing domains are closely associated with cells that subsequently differentiate into sclerenchymatous cells. These findings suggest that the function of OsYABBY1 is involved in regulating the differentiation of a few specific cell types and is unrelated to polar regulation of lateral organ development.     

Mutations in the <Emphasis Type="Italic">TORNADO2</Emphasis> gene affect cellular decisions in the peripheral zone of the shoot apical meristem of <Emphasis Type="Italic">Arabidopsis</Emphasis><Emphasis Type="Italic">thaliana</Emphasis>

Summary An EMS (ethyl methanesulfonate) mutagenesis effector screen performed with the STM:GUS marker line in Arabidopsis thaliana identified a loss-of-function allele of the TORNADO2 gene. The histological and genetic analyses described here implicate TRN2 in SAM function, where the peripheral zone in trn2 mutants is enlarged relative to the central stem cell zone. The trn2 mutant allele partially rescues the phenotype of shoot meristemless mutants but behaves additively to wuschel and clavata3 alleles during the vegetative phase and in the outer floral whorls. The development of carpels in trn2 wus-1 double mutant flowers indicates that pluripotent cells persist in floral meristems in the absence of TRN2 function and can be recruited for carpel anlagen. The data implicate a membrane-bound plant tetraspanin protein in cellular decisions in the peripheral zone of the SAM.     

Colonization of the <Emphasis Type="Italic">Arabidopsis</Emphasis> rhizosphere by fluorescent <Emphasis Type="Italic">Pseudomonas</Emphasis> spp. activates a root-specific,ethylene-responsive <Emphasis Type="Italic">PR-5</Emphasis> gene in the vascular bundle

Plants of which the roots are colonized by selected strains of non-pathogenic, fluorescent Pseudomonas spp. develop an enhanced defensive capacity against a broad spectrum of foliar pathogens. In Arabidopsis thaliana, this rhizobacteria-induced systemic resistance (ISR) functions independently of salicylic acid but requires responsiveness to jasmonic acid and ethylene. In contrast to pathogen-induced systemic acquired resistance (SAR), ISR is not associated with systemic changes in the expression of genes encoding pathogenesis-related (PR) proteins. To identify genes that are specifically expressed in response to colonization of the roots by ISR-inducing Pseudomonas fluorescens WCS417r bacteria, we screened a collection of Arabidopsis enhancer trap and gene trap lines containing a transposable element of the Ac/Ds system and the GUS reporter gene. We identified an enhancer trap line (WET121) that specifically showed GUS activity in the root vascular bundle upon colonization of the roots by WCS417r. Fluorescent Pseudomonas spp. strains P. fluorescens WCS374r and P. putida WCS358r triggered a similar expression pattern, whereas ISR-non-inducing Escherichia coli bacteria did not. Exogenous application of the ethylene precursor 1-aminocyclopropane-1-carboxylate (ACC) mimicked the rhizobacteria-induced GUS expression pattern in the root vascular bundle, whereas methyl jasmonic acid and salicylic acid did not, indicating that the Ds element in WET121 is inserted in the vicinity of an ethylene-responsive gene. Analysis of the expression of the genes in the close vicinity of the Ds element revealed AtTLP1 as the gene responsible for the in cis activation of the GUS reporter gene in the root vascular bundle. AtTLP1 encodes a thaumatin-like protein that belongs to the PR-5 family of PR proteins, some of which possess antimicrobial properties. AtTLP1 knockout mutant plants showed normal levels of WCS417r-mediated ISR against the bacterial leaf pathogen Pseudomonas syringae pv. tomato DC3000, suggesting that expression of AtTLP1 in the roots is not required for systemic expression of ISR in the leaves. Together, these results indicate that induction of AtTLP1 is a local response of Arabidopsis roots to colonization by non-pathogenic fluorescent Pseudomonas spp. and is unlikely to play a role in systemic resistance.     

<Emphasis Type="Italic">SnRK2</Emphasis> Homologs in <Emphasis Type="Italic">Gossypium</Emphasis> and <Emphasis Type="Italic">GhSnRK2.6</Emphasis> Improved Salt Tolerance in Transgenic Upland Cotton and <Emphasis Type="Italic">Arabidopsis</Emphasis>

SnRK2s are a large family of plant-specific protein kinases, which play important roles in multiple abiotic stress responses in various plant species. But the family in Gossypium has not been well studied. Here, we identified 13, 10, and 13 members of the SnRK2 family from Gossypium raimondii, Gossypium arboreum, and Gossypium hirsutum, respectively, and analyzed the locations of SnRK2 homologs in chromosomes based on genome data of cotton species. Phylogenetic tree analysis of SnRK2 proteins showed that these families were classified into three groups. All SnRK2 genes were comprised of nine exons and eight introns, and the exon distributions and the intron phase of homolog genes among different cotton species were analogous. Moreover, GhSnRK2.6 was overexpressed in Arabidopsis and upland cotton, respectively. Under salt treatment, overexpressed Arabidopsis could maintain higher biomass accumulation than wild-type plants, and GhSnRK2.6 overexpression in cotton exhibited higher germination rate than the control. So, the gene GhSnRK2.6 could be utilized in cotton breeding for salt tolerance.