Plant–plant interactions Flashcards
Describe some positive effects plants can have on each other
- accumulation of nutrients
- provision of shade
- protection from herbivores
Describe root exudates
secrete a variety of organic compounds that may indicate kinship
Describe VOCs
- produced by leaves/flowers/fruits
- can be used in defence responses
VOCs
volatile organic compounds
Give an example of competition between plants
Crops and weeds competing for resources
Describe facilitation
- ‘Helper plant’ provides benefit to another plant but does not incur any cost
- e.g. epiphytes on trees
Give an example of plant-plant co-operation
swamping predators by masting
masting
producing seeds simultaneously at no cost but with benefit to others
Describe allelopathy
- one partner benefits at the cost of the other
- release of inhibitory allelochemicals via roots affect the growth of neighbouring plants of other species
Give an example of plant-plant altruism
community supports a more elongated, taller plant in a dense stand, which both receives more light, and shades its neighbours.
Describe parasitic plants
- 4,750 of the 369,000 (1.2%) angiosperm species are parasitic
- evolved 12 times
- morphologically diverse – from trees to endoparasites
Describe the classifications of parasitic plants
- obligate root holoparasite (Orobanche)
- obligate root hemiparasite (Nuytsia)
- facultative root hemiparasite (Rhinanthus)
- obligate stem holoparasite (Cuscuta)
- obligate stem hemiparasite (Viscum)
Describe Witchweed (Striga)
destroys over $10 billion of cereals and legumes in Africa and Asia each year
Describe Broomrapes (Orobanche and Phelipanche)
problematic weeds of various crop species in southern and eastern Europe, the Middle East and North Africa.
Parasitic plants have
highly reduced plastid genomes
Describe parasitic plant genomes
- most plastid genomes are highly conserved in structure/gene content
- Epifagus virginiana lacks all genes for photosynthesis and chlororespiration found in chloroplast genomes of green plants
- The 70,028-base-pair genome contains only 42 genes, at least 38 of which specify components of the gene- expression apparatus of the plastid.
Describe the haustorium
- specialised multicellular organ shared by parasitic plants
- physiological bridge through which hormonal interactions, viruses, proteins and mRNA transcripts can be transported
List some holoparasites in the Family Orobanchaceae
- Cistanche
- Lathraea
- Lathraea
- Orobanche
- Phelipanche
List some hemiparasites in the Family Orobanchaceae
- Bartsia
- Rhinathus
- Parentucellia
Describe the Orobanchaceae
- all hemiparasites and holoparasites are monophyletic along with the autotroph Lindenbergia
- parasitism evolved only once in the lineage
- holoparasitism evolved at least 5 times independently
Holoparasitism
loss of photosynthesis
List some Orobanchaceae
- Alectra
- Striga
- Aeginetia
- Boschniaka
- Christisonia
- Cistanche
- Conopholis
- Epifagus
- Eremitilla
- Harveya
Trace the phylogeny of parasitism in plants
- autotrophic Lindenbergia
- origin of parasitism -> Triphysaria
- origin of obligate parasitism -> Striga
- origin of holoparasitism -> Orobanche
Describe endoparasites
- highly specialised group of plants (highly derived)
- unique life cycles compared to other angiosperms
- most of the vegetative portion of the parasite lives inside of its host
- emergence occurs only during flowering
- parasites avoid predatory herbivores and live in a constant environment
endoparasites
endophytic holoparasites
List some plant endoparasites
- Rafflesiaceae
- Mitrastemonaceae
- Apodanthaceae
- Cytinaceae
Describe Rafflesia patma life cycle
- proembryo composed of two tiers of cells above a single cell
- forms uniseriate filament (predominant vegetative form)
- initiation of protocorm formation by periclinal divisions give rise to a multiseriate filament
- protocorm transformed into a cormus
- young floral shoot apex emerges from the host with completely differentiated floral organs
- produces seeds
Describe Rafflesiaceae phylogeny
- mitochondrial DNA places Rafflesiaceae as a member of Malpighiales
- Euphorbiaceae
- 79-fold increase in flower diameter on the stem lineage of Rafflesiaceae
- one of the most dramatic cases of size evolution reported for eukaryotes
Describe Mitrastemon phylogeny
holoparasitic angiosperm within the order Ericales
Which lineages did holoparasitism conversantly evolve in?
- Mitrastemonaceae
- Cytinaceae
- Rafflesiaceae
- Apodanthaceae
Endophytic holoparasites are highly susceptible to
HGT
HGT and LGT make up the
non-sexual movement of genetic information between genomes
Describe HGTs in plant endoparasites
- large proportion of the mitochondrial genes pf parasitic plants
- close contact of the mitochondria at the host-parasite interface
Describe Sapria
unprecedented levels of gene loss
Discuss gene loss in endoparasitic plants
- convergence across unrelated parasitic plant groups
- convergently lost genes are enriched in functions involving photosynthesis, defence, and stress response
What mediates host specificity in parasitic plants?
multiple layers of incompatibility
Discuss mycoheterotrophy
- plants evolved to obtain carbon from other photosynthetic plants through a shared mycorrhizal network, rather than by photosynthesis.
- evolved multiple times, especially in monocots such as orchids
- plants can be mycoheterotrophic for some of their life cycle, or partially mycoheterotrophic
Give a mycoheterotroph
- Oxygyne
- Thismiaceae
Describe Rhizanthella
- flowers underground
- discovery in Western
Australia in 1928 - all known species found by accident
- pollinated by termites
- dispersed by underground marsupial mammals
