Hyaloperonospora

Hyaloperonospora is a genus of oomycete, obligate, plant pathogens that was originally considered to be part of Peronospora.[1] Species in this group produce a disease called downy mildew and can infect many important crops.[1] From the 19 downy mildew producing genera, Hyaloperonospora has been grouped with Perofascia in the brassicolous downy mildews.[1] In the group of downy mildews, Hyaloperonospora is the third biggest genus.[1] The most famous species in the genus is the Hyaloperonospora parasitica, or also known as Hyaloperonospora arabidopsis.[2] This species has become a model organism from its ability to infect the model plant Arabidopsis thaliana.[2] It is used to study plant-pathogen interactions, and is currently the only Hyaloperonospora species that has an assembled genome.[2]

Hyaloperonospora
Hyaloperonospora brassicae on cabbage
Scientific classification
Clade: SAR
Phylum: Oomycota
Order: Peronosporales
Family: Peronosporaceae
Genus: Hyaloperonospora
Constant.

History

In 2002, Hyaloperonospora was discovered and described by Constantinescu, O. and Fatehi,J. using morphological and molecular characteristics.[3] Later, Göker et al., also used molecular phylogenetic techniques showing that the group was different enough from the other Peronospora species to be its own taxon.[4] Hyaloperonospora along with Perofascia were the first downy mildews described using their molecular phylogenies.[1]

Habitat and ecology

Hyaloperonospora can be found on plants from about 20 different tribes of Brassicaceae.[1] They can generally be found anywhere their host plant grows, due to human transport from seed trade.[1] Hyaloperonospora parasitica is unlike most other species in the family in that it has a very wide host range, infecting a variety of crops. Another important interaction is with Hyaloperonospora brassicae, which also has a wider host range infecting many Brassica species.

General form and structure

Hyaloperonospora differs from Perofascia in that its sporangiophores are tree-like, its haustoria are lobate to globose, and the walls of its oospores are relatively thinner.[1]

The life history does not differ from that of Peronospora, the genus that Hyaloperonospora species used to be classified under. It begins as sporangia, which are small spore-like structure, and when it lands next to a leaf stoma, it germinates a germ-tube.[5] The germ tube enters the leaf cell creating a haustorium, which allows the mould the uptake nutrients from the leaf.[5] The mould will continue to grow, with hyphae extending into the leaf’s intercellular space.[5] This invasion kills some of the leaf cells and the leaf will develop a lesion followed by necrosis.[5] If the conditions are favourable, the mould will undergo asexual reproduction and produce a tree of sporangiophores out of the leaf.[5] The sporangiophores will produce conidia that can be dispersed by the wind to another plant.[5] If the conditions in the leaf were unfavourable, the mould can undergo sexual reproduction and produce haploid antheridia and haploid oogonia through meiosis.[5] These two structures are the only non-diploid stages of the Hyaloperonospora.[5] The antheridia will fuse to the oogonia inducing plasmogamy followed by karyogamy to form diploid oospores.[5] The oospores will then be dispersed through the wind to infect more plants.[5]

Practical importance

Hyaloperonospora arabidopsis infects the model plant Arabidopsis thaliana, and by association has become a model pathogen for studying plant-pathogen interactions.[2] Studying these interactions should give us insight into how we can more effectively protect our crops from deadly eukaryotic pathogens. It is also used as a model in the Arabidopsis eFP Browser as one of the nine biotic stresses.[6]

Genomics and genetics

The Hyaloperonospora arabidopsis genome was first sequenced and assembled in 2008 using Sanger and Illumina sequencing, by Baxter et al.[7] They reported a genome size of 78 Mb with 9.5x coverage of the nuclear genome and did not assemble the mitochondrial genome.[7] They also found that 42% of the genome consisted of repetitive elements.[7] 14,543 protein coding genes were predicted using a program to detect gene models.[7]

In 2015, two more isolates of Hyaloperonospora arabidopsis were sequenced using Illumina HiSeq with 90x coverage, and reported genome sizes of 70 Mb and 74 Mb.

Species include

  • Hyaloperonospora arabidopsidis (Gäum.) Göker, Voglmayr, Riethm., Weiss & Oberw., 2003
  • Hyaloperonospora brassicae (Gäum.) Göker, Voglmayr, Riethm., Weiss & Oberw., 2003
  • Hyaloperonospora parasitica (Pers.) Constant., 2002
  • Hyaloperonospora drabae
  • Hyaloperonospora floerkeae (Kellerm.) Constant. 2002
  • Hyaloperonospora camelinae
  • Hyaloperonospora dentariae (Rabenh.) Voglmayr 2013
  • Hyaloperonospora isatidis
  • Hyaloperonospora erophilae
  • Hyaloperonospora cardamines-enneaphyllos Voglmayr 2013
  • Hyaloperonospora cheiranthi
  • Hyaloperonospora arabidis-alpinae
  • Hyaloperonospora sisymbrii-loeselii
  • Hyaloperonospora sisymbrii-sophiae
  • Hyaloperonospora malyi (Lindtner) Voglmayr 2013
  • Hyaloperonospora tribulina (Pass.) Constant. 2002
  • Hyaloperonospora barbareae
  • Hyaloperonospora lobulariae
  • Hyaloperonospora berteroae
  • Hyaloperonospora galligena
  • Hyaloperonospora hesperidis
  • Hyaloperonospora dentariae-macrophyllae
  • Hyaloperonospora cardamines-laciniatae
  • Hyaloperonospora rorippae-islandicae
  • Hyaloperonospora lunariae
  • Hyaloperonospora cochleariae
  • Hyaloperonospora lepidii-perfoliati (Savul. & Rayss) Constant. 2002
  • Hyaloperonospora thlaspeos-perfoliati
  • Hyaloperonospora nesliae
  • Hyaloperonospora thlaspeos-arvensis
  • Hyaloperonospora cardaminopsidis
  • Hyaloperonospora nasturtii-aquatici
  • Hyaloperonospora praecox
  • Hyaloperonospora norvegica
  • Hyaloperonospora niessliana (Berl.) Constant. 2002

References
  1. Thines, M., & Choi, Y. J. (2015). "Evolution, diversity, and taxonomy of the Peronosporaceae, with focus on the genus Peronospora". Phytopathology. 106 (1): 6–18. doi:10.1094/PHYTO-05-15-0127-RVW. PMID 26649784.CS1 maint: multiple names: authors list (link)
  2. Coates, M. E., & Beynon, J. L. (2010). "Hyaloperonospora arabidopsidis as a pathogen model". Annual Review of Phytopathology. 48: 329–45. doi:10.1146/annurev-phyto-080508-094422. PMID 19400636.CS1 maint: multiple names: authors list (link)
  3. Constantinescu, O. & Fatehi,J. (2002). "Peronospora-like fungi (Chromista, Peronosporales) parasitic on Brassicaceae and related hosts". Nova Hedwigia. 74: 291–338. doi:10.1127/0029-5035/2002/0074-0291.CS1 maint: multiple names: authors list (link)
  4. Göker, M., Voglmayr, H., Riethmüller, A., Weiß, M., & Oberwinkler, F. (2003). "Taxonomic aspects of Peronosporaceae inferred from Bayesian molecular phylogenetics". Canadian Journal of Botany. 81 (7): 672–683. doi:10.1139/b03-066.CS1 maint: multiple names: authors list (link)
  5. Krsteska, V., Dimeska, V., Stojkov, S., & Stojanoski, P. (2015). "Peronospora tabacina A. the causing agent of Blue Mold disease on tobacco". Bulgarian Journal of Agricultural Science. 21: 132–139.CS1 maint: multiple names: authors list (link)
  6. Winter, D., Vinegar, B., Nahal, H., Ammar, R., Wilson, G. V., & Provart, N. J. (2007). "An "Electronic Fluorescent Pictograph" browser for exploring and analyzing large-scale biological data sets". PLOS ONE. 2 (8): e718. doi:10.1371/journal.pone.0000718. PMC 1934936. PMID 17684564.CS1 maint: multiple names: authors list (link)
  7. Baxter, L., Tripathy, S., Ishaque, N., Boot, N., Cabral, A., Kemen, E., ... & Bittner-Eddy, P. (2010). "Signatures of adaptation to obligate biotrophy in the Hyaloperonospora arabidopsidis genome". Science. 330 (6010): 1549–1551. doi:10.1126/science.1195203. PMC 3971456. PMID 21148394.CS1 maint: multiple names: authors list (link)
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