Non-canonical structure, function and phylogeny of the Bsister MADS-box geneOsMADS30of rice (Oryza sativa)

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Abstract

Bsister MADS-box genes play key roles in female reproductive organ and seed development throughout seed plants. This view is supported by their high conservation in terms of sequence, expression and function. In grasses, there are three subclades of Bsister genes: theOsMADS29-, theOsMADS30- and theOsMADS31-like genes. Here, we report on the evolution of theOsMADS30-like genes. Our analyses indicate that these genes evolved under relaxed purifying selection and are rather weakly expressed.OsMADS30, the representative of theOsMADS30-like genes from rice (Oryza sativa), shows strong sequence deviations in its 3′ region when compared to orthologues from other grass species. We show that this is due to a 2.4-kbp insertion, possibly of a hitherto unknown helitron, which confers a heterologous C-terminal domain toOsMADS30. This putative helitron is not present in theOsMADS30orthologues from closely related wild rice species, pointing to a relatively recent insertion event. Unlike other Bsister mutantsO. sativaplants carrying a T-DNA insertion in theOsMADS30gene do not show aberrant seed phenotypes, indicating thatOsMADS30likely does not have a canonical ‘Bsister function’. However, imaging-based phenotyping of the T-DNA carrying plants revealed alterations in shoot size and architecture. We hypothesize that sequence deviations that accumulated during a period of relaxed selection in the gene lineage that led toOsMADS30and the alteration of the C-terminal domain might have been a precondition for a potential neo-functionalization ofOsMADS30inO. sativa.

Significance Statement

Gene duplications can lead to neo-functionalization or sub-functionalization of one duplicate. Bsister genes are highly conserved MADS-box genes involved in ovule and seed development. Here we present molecular phylogenetic analysis ofOsMADS30-like Bsister genes from monocots, suggesting that many evolved under relaxed selection. Surprisingly, relaxed selection might have facilitated neo-functionalization forOsMADS30, whose mutant shows an unexpected vegetative phenotype.

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