How did the ancestors of bananas, coconuts, rice, and corn evolve?

Important horticultural crops such as bananas, asparagus, coconuts, or bulk food crops such as rice, wheat, and corn are monocotyledonous plants. Monocotyledonous plants are one of the important branches of angiosperms, accounting for about one-fifth of the species diversity of angiosperms.

Recently, the research team of wuhan botanical garden of the Chinese Academy of Sciences and French collaborators announced the genome of calamus calamus, an important aquatic medicinal plant in the order calamus, the earliest branch of monocotyledonous plants, and the study revealed the early genome evolution process and law of the ancestors of monocotyledonous plants, and the relevant results were published in Nature-Plants.


Stone calamus Shi Tao courtesy of the picture

The morphological characteristics of monocotyledonous plants, such as roots and leaf veins, are obviously different from other angiosperms, and the early origin of its ancestors is one of the hot issues of plant evolutionary biology.

The earliest fossil record of monocotyledonous plants dates back to the early Cretaceous period. Shi Tao, the first author of the paper and an associate researcher at Wuhan Botanical Garden, introduced that many basal monocotyledonous plants, such as calamus, Zephyllaceae, water turtles, etc., are mostly aquatic and wet plants, so some scientists have proposed that the ancestors of monocotyledonous plants originated in the aquatic environment. However, this hypothesis has always lacked evidence of paleontology and genomic evolution.

“Calamus is the earliest extant clade of monocotyledonous plants and is a sister group to all other monocotyledonous plants.” Shi Tao said that this special “status” makes calamus species an important material for exploring and revealing the early evolution of monocotyledonous plants.

In this study, the Wuhan Botanical Garden, in collaboration with the French National Institute of Agri-Food and Environment, used PacBio and Hi-C technology to complete whole genome sequencing and chromosomal-level assembly of calamus spp. Through genome-wide comparative analysis with other monocotyledonous plants, the researchers found that calamus had experienced only one independent paleoploidy event with subgenomic dominance effects.

“Genome-wide duplication or paleoclexis is common during the radiation differentiation of monocotyledonous plants, and it is also considered to be one of the key mechanisms for promoting species diversification and adaptation to the environment.” Shi Tao explained that the greater the number of paleoploids, the higher the species diversity.

The study also found that both the structural evolution of the calamus genome and the rate of amino acid sequence replacement showed slow and conserved characteristics. Shi Tao said that this also confirms the previous speculation of the research team that the more basal species, the more conservative the evolution.

Further correlation analysis shows that the relatively conservative collinear structure of the genomes of each species is significantly related to its sequence replacement rate and the number of genome doublings, which Shi Tao believes may also be the reason for the relatively slow evolution of the genome structure of Calamus spp.

In addition, the researchers identified some important functional gene family evolution events that are associated with the early morphological evolution of monocotyledonous plants and adaptation to wetlands or aquatic habitats.

For example, Shi Tao has shown that past studies have shown that the DOT3 gene in Arabidopsis thaliana, if functionally missing, can lead to defects in seedling and primary root growth, and produce abnormal parallel veining in young leaves. “Now we have found that this gene is lost in both monocotyledonous plants and aquatic water lilies, which may be related to specific traits such as parallel/palmate leaf veins and degeneration of primary roots in these two taxa.” (Source: China Science Daily Hu Minqi)

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