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Weird plants
For the first time, this extraordinary compilation showcases weird, mysterious and bizarre plants from around the world. Plants trick, kill, steal and kidnap, and this unique book explores a fascinating world in which plants have turned the tables on animals. Author Chris Thorogood showcases these plant behaviors, the interrelationships among plants, the interdependencies between plants and animals, and the intrigue of plant evolution. All types of weird and sinister creatures are featured in this book, from carnivorous plants that drug, drown and consume unsuspecting insect prey; giant pitcher plants that have evolved toilets for tree shrews; flowers that mimic rotting flesh to attract pollinating flies, and orchids that duplicitously look, feel and even smell like a female insect to bamboozle sex-crazed male bees.
Book
Parasitic angiosperms
Angiosperms that morphologically and physiologically attach to other flowering plants by means of a haustorium have evolved 12 times independently resulting in 292 genera and ca. 4750 species. Although hemiparasites predominate, holoparasitism has evolved in all but two clades, Cassytha (Lauraceae) and Krameria (Krameriaceae). Santalales contains the largest number of genera (179) and species (2428) among the 12 parasitic plant lineageswhereas Orobanchaceae is the largest single family with 102 genera and over 2100 species. This review presents the current state of knowledge on the molecular phylogenetic relationships among all clades of parasitic angiosperms. These methods have been particularly important in revealing the closest non-parasitic relatives of holoparasites, plants that exhibit reduced morphologies, increased substitution rates, and frequent horizontal gene transfers, all of which confound phylogenetics. Although comprehensive molecular phylogenies are still lacking for many of the large genera, nearly complete generic level sampling exists, thus allowing unprecedented understanding of the evolutionary relationships within and among these fascinating plants.
Journal Article
The Path from β-Carotene to Carlactone, a Strigolactone-Like Plant Hormone
Germination of parasitic witchweeds depends on strigolactones, which also regulate plant branching and signal in the context of mycorrhizal symbioses. The biosynthetic pathways that lead to strigolactones are founded in carotenoid biosynthesis, but further steps have been obscure. Alder et al. (p. 1348 ) have now identified a biochemical pathway that generates a strigolactone-like compound, carlactone, which shows biological actions similar to those of strigolactone. Elucidation of the biosynthetic pathway of a new plant hormone variant that may be useful in agricultural settings is shown. Strigolactones, phytohormones with diverse signaling activities, have a common structure consisting of two lactones connected by an enol-ether bridge. Strigolactones derive from carotenoids via a pathway involving the carotenoid cleavage dioxygenases 7 and 8 (CCD7 and CCD8) and the iron-binding protein D27. We show that D27 is a β-carotene isomerase that converts all- trans -β-carotene into 9- cis -β-carotene, which is cleaved by CCD7 into a 9-cis–configured aldehyde. CCD8 incorporates three oxygens into 9- cis -β-apo-10′-carotenal and performs molecular rearrangement, linking carotenoids with strigolactones and producing carlactone, a compound with strigolactone-like biological activities. Knowledge of the structure of carlactone will be crucial for understanding the biology of strigolactones and may have applications in combating parasitic weeds.
Journal Article
Strigolactone inhibition of shoot branching
A carotenoid-derived hormonal signal that inhibits shoot branching in plants has long escaped identification. Strigolactonesare compounds thought to be derived from carotenoids and are known to trigger the germination of parasitic plant seeds andstimulate symbiotic fungi. Here we present evidence that carotenoid cleavage dioxygenase 8 shoot branching mutants of peaare strigolactone deficient and that strigolactone application restores the wild-type branching phenotype to ccd8 mutants.Moreover, we show that other branching mutants previously characterized as lacking a response to the branching inhibitionsignal also lack strigolactone response, and are not deficient in strigolactones. These responses are conserved in Arabidopsis.In agreement with the expected properties of the hormonal signal, exogenous strigolactone can be transported in shoots andact at low concentrations. We suggest that endogenous strigolactones or related compounds inhibit shoot branching inplants. Furthermore, ccd8 mutants demonstrate the diverse effects of strigolactones in shoot branching, mycorrhizalsymbiosis and parasitic weed interaction.
Journal Article
CYP722C from Gossypium arboreum catalyzes the conversion of carlactonoic acid to 5-deoxystrigol
Main conclusion
CYP722C from cotton, a homolog of the enzyme involved in orobanchol synthesis in cowpea and tomato, catalyzes the conversion of carlactonoic acid to 5-deoxystrigol.
Strigolactones (SLs) are important phytohormones with roles in the regulation of plant growth and development. These compounds also function as signaling molecules in the rhizosphere by interacting with beneficial arbuscular mycorrhizal fungi and harmful root parasitic plants. Canonical SLs, such as 5-deoxystrigol (5DS), consist of a tricyclic lactone ring (ABC-ring) connected to a methylbutenolide (D-ring). Although it is known that 5DS biosynthesis begins with carlactonoic acid (CLA) derived from β-carotene, the enzyme that catalyzes the conversion of CLA remains elusive. Recently, we identified cytochrome P450 (CYP) CYP722C as the enzyme that catalyzes direct conversion of CLA to orobanchol in cowpea and tomato (Wakabayashi et al., Sci Adv 5:eaax9067, 2019). Orobanchol has a different C-ring configuration from that of 5DS. The present study aimed to characterize the homologous gene, designated
GaCYP722C,
from cotton (
Gossypium arboreum
) to examine whether this gene is involved in 5DS biosynthesis. Expression of
GaCYP722C
was upregulated under phosphate starvation, which is an SL-producing condition. Recombinant GaCYP722C was expressed in a baculovirus-insect cell expression system and was found to catalyze the conversion of CLA to 5DS but not to 4-deoxyorobanchol. These results strongly suggest that GaCYP722C from cotton is a 5DS synthase and that CYP722C is the crucial CYP subfamily involved in the generation of canonical SLs, irrespective of the different C-ring configurations.
Journal Article
Strigolactone biosynthesis catalyzed by cytochrome P450 and sulfotransferase in sorghum
• Root parasitic plants such as Striga, Orobanche, and Phelipanche spp. cause serious damage to crop production world-wide. Deletion of the Low Germination Stimulant 1 (LGS1) gene gives a Striga-resistance trait in sorghum (Sorghum bicolor). The LGS1 gene encodes a sulfotransferase-like protein, but its function has not been elucidated.
• Since the profile of strigolactones (SLs) that induce seed germination in root parasitic plants is altered in the lgs1 mutant, LGS1 is thought to be an SL biosynthetic enzyme. In order to clarify the enzymatic function of LGS1, we looked for candidate SL substrates that accumulate in the lgs1 mutants and performed in vivo and in vitro metabolism experiments.
• We found the SL precursor 18-hydroxycarlactonoic acid (18-OH-CLA) is a substrate for LGS1. CYP711A cytochrome P450 enzymes (SbMAX1 proteins) in sorghum produce 18-OH-CLA. When LGS1 and SbMAX1 coding sequences were co-expressed in Nicotiana benthamiana with the upstream SL biosynthesis genes from sorghum, the canonical SLs 5-deoxystrigol and 4-deoxyorobanchol were produced.
• This finding showed that LGS1 in sorghum uses a sulfo group to catalyze leaving of a hydroxyl group and cyclization of 18-OH-CLA. A similar SL biosynthetic pathway has not been found in other plant species.
Journal Article
The recent expansion of the invasive hemiparasitic plant Cassytha filiformis and the reciprocal effect with its main hosts
Cassytha filiformis
is a hemiparasitic plant that causes severe effects in its host plants
.
Since this decade, this alien species has been increasing its distribution towards the coastal areas of the Peninsula of Yucatán, parasitizing shrub species that play a crucial role in the containment of soil erosion. Here we studied the current distribution of
C. filiformis
along the coastal dune in northern Yucatán, recording the frequency of parasitism and the identity of its host plants. In addition, we evaluated the effect of
C. filiformis
on the sexual reproductive success of the main host plants and the effect of host species identity on
C. filiformi’s
reproductive success. We found that the distribution of
C. filiformis
occurs throughout the coastal dunes of Yucatan (covering ≈250 km), parasitizing 15 species. However,
ca
. 70% of
C. filiformis
plants occur on three common shrub species:
Suriana maritima
,
Scaevola plumieri
, and
Tournefortia gnaphalodes
. The frequency of parasitized plants by
C. filiformis
was not dependent on host plant abundance.
Tournefortia gnaphalodes
suffer a higher proportion of parasitism. The reproductive success of the three host plants was lower in the presence of the parasitic plant. On the other hand,
C. filiformis
showed higher reproductive success when parasitizing
S. maritima.
Our results suggest that
C. filiformis
has extensively invaded the Yucatán coastal dunes, significantly reducing the sexual reproduction of its host-plant species. Overall, our results suggest that
C. filiformis
has the potential to cause significant damage in the Yucatán coastal dune community.
Journal Article
Seed germination in parasitic plants: what insights can we expect from strigolactone research?
This review discusses how current knowledge about the molecular mechanisms governing strigolactone-induced seed germination of obligate root-parasitic plants can be used to combat these threats to crops.
Abstract
Obligate root-parasitic plants belonging to the Orobanchaceae family are deadly pests for major crops all over the world. Because these heterotrophic plants severely damage their hosts even before emerging from the soil, there is an unequivocal need to design early and efficient methods for their control. The germination process of these species has probably undergone numerous selective pressure events in the course of evolution, in that the perception of host-derived molecules is a necessary condition for seeds to germinate. Although most of these molecules belong to the strigolactones, structurally different molecules have been identified. Since strigolactones are also classified as novel plant hormones that regulate several physiological processes other than germination, the use of autotrophic model plant species has allowed the identification of many actors involved in the strigolactone biosynthesis, perception, and signal transduction pathways. Nevertheless, many questions remain to be answered regarding the germination process of parasitic plants. For instance, how did parasitic plants evolve to germinate in response to a wide variety of molecules, while autotrophic plants do not? What particular features are associated with their lack of spontaneous germination? In this review, we attempt to illustrate to what extent conclusions from research into strigolactones could be applied to better understand the biology of parasitic plants.
Journal Article
Cuscuta australis (dodder) parasite eavesdrops on the host plants’ FT signals to flower
Many plants use environmental cues, including seasonal changes of day length (photoperiod), to control their flowering time. Under inductive conditions, FLOWERING LOCUS T (FT) protein is synthesized in leaves, and FT protein is a mobile signal, which is able to travel to the shoot apex to induce flowering. Dodders (Cuscuta, Convolvulaceae) are root- and leafless plants that parasitize a large number of autotrophic plant species with varying flowering time. Remarkably, some dodder species, e.g., Cuscuta australis, are able to synchronize their flowering with the flowering of their hosts. Detailed sequence inspection and expression analysis indicated that the FT gene in dodder C. australis very likely does not function in activating flowering. Using soybean host plants cultivated under inductive and noninductive photoperiod conditions and soybean and tobacco host plants, in which FT was overexpressed and knocked out, respectively, we show that FT-induced flowering of the host is likely required for both host and parasite flowering. Biochemical analysis revealed that host-synthesized FT signals are able to move into dodder stems, where they physically interact with a dodder FD transcription factor to activate dodder flowering. This study demonstrates that FTs can function as an important interplant flowering signal in host–dodder interactions. The unique means of flowering regulation of dodder illustrates how regressive evolution, commonly found in parasites, may facilitate the physiological synchronization of parasite and host, here allowing the C. australis parasite to time reproduction exactly with that of their hosts, likely optimizing parasite fitness.
Journal Article
Parasitic Weeds: A World Challenge
While witchweed is nearing eradication in the United States, it continues to thrive in other parts of the world, especially in Africa, together with other witchweed species. The continuing problems from witchweeds and other parasitic weeds, the broomrapes, dodders and mistletoes, are outlined, including their extent, the degrees of damage caused, and the difficulties in their control. While a small minority are being successfully controlled by the use of immune varieties, most are currently controlled by existing techniques only partially, or on a local basis, and they may even be spreading or intensifying. The challenges they present are emphasised.
Journal Article