About 1% of flowering plants are parasitic, exhibiting fascinating adaptations and behaviors. Recent research indicates that some of these plants are evolving to become highly reliant on their host plants, to the extent that they’re discarding significant portions of their genomes linked to fundamental processes like photosynthesis.
These observations are detailed in a study released on September 21 in the journal Nature Plants.
The Balanophoraceae plant family, found across temperate and tropical regions in Asia and Africa, often mirrors fungi that grow around tree roots. But there’s more than what’s visible. What might seem like mushroom-like structures are in fact inflorescences or clusters of meticulously organized flowers on a stalk.
Distinctively, while most parasitic plants use a thin extension known as a haustorium to tap into a host and extract nutrients, those from the Balanophora genus compel their host plant’s vascular system to form a tuber for nutrient storage. This results in a distinctive subterranean organ composed of tissue from both the host and the Balanophora, which the latter feeds on.
A collaboration between the Beijing Genomics Institute (BGI) and the University of British Columbia set out to understand the evolutionary journey of these plants by comparing the genomes of Balanophora with another parasitic plant genus, Sapria. The latter, part of the Rafflesiaceae family, includes some notably pungent corpse flowers and is generally found in Asia’s tropical forests.
Remarkably, the study revealed that while evolving their parasitic strategies, Sapria shed 38% of its genome, and Balanophora reduced theirs by 28%. This, as per the researchers, signifies an unprecedented genome reduction among flowering plants.
Both plant types, Balanophora and Sapria, have also nearly eradicated all genes tied to photosynthesis and other vital functions, such as nitrogen uptake, root formation, and flower development regulation.
Given these plants derive sustenance from their host plants and aren’t dependent on sunlight and water for food production, they seem to be discarding these genes.
Interestingly, the genes tied to the production of a primary hormone, abscisic acid (ABA)—key for plant stress reactions and signaling—have been discarded in both plants. Despite this loss, the researchers noted an accumulation of the ABA hormone in Balanophora’s flowering stems.
Furthermore, genes linked to ABA response remain intact in these parasitic plants. The team believes that this gene loss could offer an evolutionary advantage.
This study illuminates the extensive genomic shifts in parasitic plants and holds significance, especially in the broader endeavor aiming to sequence the genomes of 10,000 plant species, termed the 10KP project.