Abstract
Around 1% of angiosperms are parasitic plants. Their growth and development solely or partly depend on host plants from which they extract water, nutrients, and other molecules using a parasitic plant-specific organ, the haustorium. Strong depletion of nutrients can result in serious growth retardation and in some cases, death of the hosts. The genus Cuscuta (dodder) comprises about 200 holoparasitic species occurring on all continents. Their seedlings have no roots and cotyledons but are only string-like hypocotyls. When they contact suitable host plants, haustoria are formed and thereafter seedlings rapidly develop into vigorously growing branches without roots and leaves. This highly specialized lifestyle suggests that Cuscuta plants likely have unique physiology in development and stress responses. Using germination and seedling growth assays, we show that C. australis seeds and seedlings are highly insensitive to abscisic acid (ABA). Transcriptome analysis and protein sequence alignment with Arabidopsis, tomato, and rice homologs revealed that C. australis most likely consists of only four functional ABA receptors. Given that Cuscuta plants are no longer severely challenged by drought stress, we hypothesize that the ABA-mediated drought resistance pathway in Cuscuta spp. might have had degenerated over time during evolution.
Highlights
Parasites are defined as organisms that obtain nutrients from hosts and cause harm but not immediate death [1]
Transcriptome data-mining suggested that C. australis likely had only 4 functional abscisic acid (ABA) receptors and this is much less than those in Arabidopsis, tomato, and rice. These data suggest that C. australis has a distinct ABA hormonal physiology, and we propose that the highly adapted and specialized lifestyle may have relaxed the selection pressure from drought stress in C. australis and have led to loss of responses to ABA
It is possible that, since they evolved parasitism, Cuscuta plants are no longer strongly challenged by drought stress
Summary
Parasites are defined as organisms that obtain nutrients from hosts and cause harm but not immediate death [1]. Plant parasitism is thought to have evolved independently at least 12 or 13 times and it was estimated that about 1% of angiosperm plants are parasitic [2]. Parasitic plants have unique physiology, ecology, and evolution. Cuscuta Response to Abscisic Acid a special organ, haustorium, which penetrates the host tissues and forms a connection between the host and parasite, parasitic plants draw nutrients and other molecules from hosts. The growth and development of parasitic plants are solely or partly dependent on the hosts
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