The embryonic leaf identity gene FUSCA3 regulates vegetative phase transitions by negatively modulating ethylene-regulated gene expression in Arabidopsis

<p>Abstract</p> <p>Background</p> <p>The embryonic temporal regulator <it>FUSCA3 </it>(<it>FUS3</it>) plays major roles in the establishment of embryonic leaf identity and the regulation of developmental timing. Loss-of-function mutations of this B3 domain transcription factor result in replacement of cotyledons with leaves and precocious germination, whereas constitutive misexpression causes the conversion of leaves into cotyledon-like organs and delays vegetative and reproductive phase transitions.</p> <p>Results</p> <p>Herein we show that activation of FUS3 after germination dampens the expression of genes involved in the biosynthesis and response to the plant hormone ethylene, whereas a loss-of-function <it>fus3 </it>mutant shows many phenotypes consistent with increased ethylene signaling. This <it>FUS3</it>-dependent regulation of ethylene signaling also impinges on timing functions outside embryogenesis. Loss of <it>FUS3 </it>function results in accelerated vegetative phase change, and this is again partially dependent on functional ethylene signaling. This alteration in vegetative phase transition is dependent on both embryonic and vegetative <it>FUS3 </it>function, suggesting that this important transcriptional regulator controls both embryonic and vegetative developmental timing.</p> <p>Conclusion</p> <p>The results of this study indicate that the embryonic regulator <it>FUS3 </it>not only controls the embryonic-to-vegetative phase transition through hormonal (ABA/GA) regulation but also functions postembryonically to delay vegetative phase transitions by negatively modulating ethylene-regulated gene expression.</p

Genome Sequence of Striga asiatica Provides Insight into the Evolution of Plant Parasitism

Parasitic plants in the genus Striga, commonly known as witchweeds, cause major crop losses in sub-Saharan Africa and pose a threat to agriculture worldwide. An understanding of Striga parasite biology, which could lead to agricultural solutions, has been hampered by the lack of genome information. Here, we report the draft genome sequence of Striga asiatica with 34,577 predicted protein-coding genes, which reflects gene family contractions and expansions that are consistent with a three-phase model of parasitic plant genome evolution. Striga seeds germinate in response to host-derived strigolactones (SLs) and then develop a specialized penetration structure, the haustorium, to invade the host root. A family of SL receptors has undergone a striking expansion, suggesting a molecular basis for the evolution of broad host range among Striga spp. We found that genes involved in lateral root development in non-parasitic model species are coordinately induced during haustorium development in Striga, suggesting a pathway that was partly co-opted during the evolution of the haustorium. In addition, we found evidence for horizontal transfer of host genes as well as retrotransposons, indicating gene flow to S. asiatica from hosts. Our results provide valuable insights into the evolution of parasitism and a key resource for the future development of Striga control strategies.Peer reviewe

The FRIABLE1 Gene Product Affects Cell Adhesion in Arabidopsis

Cell adhesion in plants is mediated predominantly by pectins, a group of complex cell wall associated polysaccharides. An Arabidopsis mutant, friable1 (frb1), was identified through a screen of T-DNA insertion lines that exhibited defective cell adhesion. Interestingly, the frb1 plants displayed both cell and organ dissociations and also ectopic defects in organ separation. The FRB1 gene encodes a Golgi-localized, plant specific protein with only weak sequence similarities to known proteins (DUF246). Unlike other cell adhesion deficient mutants, frb1 mutants do not have reduced levels of adhesion related cell wall polymers, such as pectins. Instead, FRB1 affects the abundance of galactose- and arabinose-containing oligosaccharides in the Golgi. Furthermore, frb1 mutants displayed alteration in pectin methylesterification, cell wall associated extensins and xyloglucan microstructure. We propose that abnormal FRB1 action has pleiotropic consequences on wall architecture, affecting both the extensin and pectin matrices, with consequent changes to the biomechanical properties of the wall and middle lamella, thereby influencing cell-cell adhesion

Arabidopsis ETHYLENE RESPONSE FACTOR 8 (ERF8) has dual functions in ABA signaling and immunity

Background: ETHYLENE RESPONSE FACTOR (ERF) 8 is a member of one of the largest transcription factor families in plants, the APETALA2/ETHYLENE RESPONSIVE FACTOR (AP2/ERF) superfamily. Members of this superfamily have been implicated in a wide variety of processes such as development and environmental stress responses. Results: In this study we demonstrated that ERF8 is involved in both ABA and immune signaling. ERF8 overexpression induced programmed cell death (PCD) in Arabidopsis and Nicotiana benthamiana. This PCD was salicylic acid (SA)-independent, suggesting that ERF8 acts downstream or independent of SA. ERF8-induced PCD was abolished by mutations within the ERF-associated amphiphilic repression (EAR) motif, indicating ERF8 induces cell death through its transcriptional repression activity. Two immunity-related mitogen-activated protein kinases, MITOGEN-ACTIVATED PROTEIN KINASE 4 (MPK4) and MPK11, were identified as ERF8-interacting proteins and directly phosphorylated ERF8 in vitro. Four putative MPK phosphorylation sites were identified in ERF8, one of which (Ser103) was determined to be the predominantly phosphorylated residue in vitro, while mutation of all four putative phosphorylation sites partially suppressed ERF8-induced cell death in N. benthamiana. Genome-wide transcriptomic analysis and pathogen growth assays confirmed a positive role of ERF8 in mediating immunity, as ERF8 knockdown or overexpression lines conferred compromised or enhanced resistance against the hemibiotrophic bacterial pathogen Pseudomonas syringae, respectively. Conclusions: Together these data reveal that the ABA-inducible transcriptional repressor ERF8 has dual roles in ABA signaling and pathogen defense, and further highlight the complex influence of ABA on plant-microbe interactions.Other UBCNon UBCReviewedFacult

Xyloglucan oligosaccharide mass profile (OLIMP) of crude cell wall material from shoots (A, B, C) and its respective 4 M KOH fractions (D, E, F).

<p>A. and D. Representative spectra derived from <i>FRB1</i>. B. and E. Representative spectra derived from <i>frb1</i>. C. OLIMP analysis of shoots. D. OLIMP analysis of 4 M KOH fraction derived from shoots. Nomenclature of xyloglucan oligosaccharides are taken from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0042914#pone.0042914-Neumetzler1" target="_blank">[38]</a> and references within. Stars indicate significant alterations with p<0.05.</p

Phenotypic variation in <i>frb1</i> mutant seedlings.

<p>A. Wild-type <i>FRB1</i> seedling after 5 days growth on MS media. B. A 3-day old <i>frb1–1</i> seedling where the hypocotyl has spontaneously broken during germination. C. An example of a <i>frb1–1</i> seedling where the cotyledons have become fused as the seedling germinated. D. A <i>frb1–2</i> seedling showing severe cell dissociation. E. A two week old <i>FRB1</i> seedling grown on MS media. F. and G. At the same stage of growth as seedlings in E, <i>frb1–1</i> and <i>frb1–2</i> seedlings have little cell separation but many do have extensive fusions between leaves and other aerial organs. All scale bars equal 0.5. mm.</p

Sugar composition and sugar incorporation in membrane preparations from <i>FRB1</i> and <i>frb1</i> plants.

<p>A. Sugar composition derived from microsomal preparations of wild-type and <i>frb1</i>–<i>2</i>. Monosaccharides and uronic acids were identified based on retention time and comparison to pure standards and values are expressed in % of total area. Significant changes (two-tailed Student's t-test, n = 3, *: p<0.05; **: p<0.01) are marked with stars. Rha: rhamnose, Ara: arabinose, Gal: galacatose, Glc: glucose, Xyl-Man: unseparated peak containing xylose and mannose, GalA: galacturonic acid, GlcA: glucuronic acid. B. The total radioactivity in the chloroform insoluble material. C. The total radioactivity in the chloroform soluble material. See the experimental procedures for details.</p