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]
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]
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[citation needed]. Another important interaction is with Hyaloperonospora brassicae, which also has a wider host range infecting many Brassica species[citation needed].
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[citation needed]. 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]
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]