Abstract
BackgroundPlant transitions to land require robust cell walls for regulatory adaptations and to resist changing environments. Cell walls provide essential plasticity for plant cell division and defense, which are often conferred by the expansin superfamily with cell wall-loosening functions. However, the evolutionary mechanisms of expansin during plant terrestrialization are unclear.ResultsHere, we identified 323 expansin proteins in 12 genomes from algae to angiosperms. Phylogenetic evolutionary, structural, motif gain and loss and Ka/Ks analyses indicated that highly conserved expansin proteins were already present in algae and expanded and purified after plant terrestrialization. We found that the expansion of the FtEXPA subfamily was caused by duplication events and that the functions of certain duplicated genes may have differentiated. More importantly, we generated space-time expression profiles and finally identified five differentially expressed FtEXPs in both large and small fruit Tartary buckwheat that may regulate fruit size by responding to indoleacetic acid.ConclusionsA total of 323 expansin proteins from 12 representative plants were identified in our study during terrestrialization, and the expansin family that originated from algae expanded rapidly after the plants landed. The EXPA subfamily has more members and conservative evolution in angiosperms. FtEXPA1, FtEXPA11, FtEXPA12, FtEXPA19 and FtEXPA24 can respond to indole-3-acetic acid (IAA) signals and regulate fruit development. Our study provides a blueprint for improving the agronomic traits of Tartary buckwheat and a reference for defining the evolutionary history of the expansin family during plant transitions to land.
Highlights
Plant transitions to land require robust cell walls for regulatory adaptations and to resist changing environments
Global identification and evolution of Expansin proteins from algae to land plants To further understand the evolutionary history of expansin during plant transitions to land, we identified 323 expansin genes by using BLAST and profile hidden Markov model (HMM) searches of two algae (Chlamydomonas reinhardtii and Volvox carteri); three bryophytes (Marchantia polymorpha, Physcomitrella patens and Sphagnum palustre); early angiosperms (Amborella trichopoda); two monocotyledons (Oryza sativa and Zea mays) and four dicotyledons (F. tataricum, Arabidopsis, Vitis vinifera and Coffea arabica) (Fig. 1, Table S1)
Up to 32 members of the EXPA subfamily were found in M. polymorpha, while other subfamily members were not Analysis of phylogeny and evolution suggests that the FtEXP in EXPA family (FtEXPA) subfamily has rich members and special structures We identified 37 expansin proteins in the Tartary buckwheat genome and assembled the basic information for these genes, such as molecular weight (Mw), PI, subcellular localization, CDS and protein sequence (Table S3-4)
Summary
Plant transitions to land require robust cell walls for regulatory adaptations and to resist changing environments. Land plant radiation and colonization are important keystones in the evolutionary history of living organisms, which have created the ecological diversity on Earth that we see today This transition was accompanied by complex and long biological evolution, which included morphological, physiological, and genetic changes, to cope with the terrestrial environment and its challenging conditions [1, 2]. The cell wall plays a key role in plant growth and development, material transport, pathogen resistance, cell division and differentiation, organ senescence and shedding. It provides the necessary mechanical support for plant cells and the plasticity that is necessary for protection against external intrusion [3, 4]. It has significant functionality in many stages of plant growth and development [7], such as stem growth and internode elongation [8], fruit ripening [9], seed germination [10], control of flowering time and flower size [11], root growth [12] and leaf development [13]
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