Search

Summary In most sexually reproducing plants, a single somatic, sub-epidermal cell in an ovule is selected to differentiate into a megaspore mother cell, which is committed to giving rise to the female germline. However, it remains unclear how intercellular signaling among somatic cells results in only one cell in the sub-epidermal layer differentiating into the megaspore mother cell. Here we uncovered a role of the THO complex in restricting the megaspore mother cell fate to a single cell. Mutations in TEX1 , HPR1 , and THO6 , components of the THO/TREX complex, led to the formation of multiple megaspore mother cells, which were able to initiate gametogenesis. We demonstrated that TEX1 repressed the megaspore mother cell fate by promoting the biogenesis of TAS3 -derived trans -acting small interfering RNA (ta-siRNA), which represses ARF3 expression. The TEX1 protein was present in epidermal cells, but not in the germline, and, through TAS3 -derived ta-siRNA, restricted ARF3 expression to the medio domain of ovule primordia. Expansion of ARF3 expression into lateral epidermal cells in a TAS3 ta-siRNA-insensitive mutant led to the formation of supernumerary megaspore mother cells, suggesting that TEX1- and TAS3- mediated restriction of ARF3 expression limits excessive megaspore mother cell formation non-cell-autonomously. Our findings reveal the role of a small-RNA pathway in the regulation of female germline specification in Arabidopsis . [ABSTRACT FROM AUTHOR]

Deposition of the histone variant H2A.Z at gene bodies regulates transcription by modifying chromatin accessibility in plants. However, the role of H2A.Z enrichment at the promoter and enhancer regions is unclear, and how H2A.Z interacts with other mechanisms of chromatin modification to regulate gene expression remains obscure. Here, we mapped genome-wide H2A.Z, H3K4me3, H3K27me3, Pol II, and nucleosome occupancy in Arabidopsis inflorescence. We showed that H2A.Z preferentially associated with H3K4me3 at promoters, while it was found with H3K27me3 at enhancers, and that H2A.Z deposition negatively correlated with gene expression. In addition, we demonstrated that H2A.Z represses gene expression by establishing low gene accessibility at +1 nucleosome and maintaining high gene accessibility at −1 nucleosome. We further showed that the high measures of gene responsiveness correlate with the H2A.Z-associated closed +1 nucleosome structure. Moreover, we found that H2A.Z represses enhancer activity by promoting H3K27me3 and preventing H3K4me3 histone modifications. This study provides a framework for future studies of H2A.Z functions and opens up new aspects for decoding the interplay between chromatin modification and histone variants in transcriptional control. [ABSTRACT FROM AUTHOR]

Studying the independent evolution of similar traits provides valuable insights into the ecological and genetic factors driving phenotypic evolution. 1 The transition from outcrossing to self-fertilization is common in plant evolution 2 and is often associated with a reduction in floral attractive features such as display size, chemical signals, and pollinator rewards. 3 These changes are believed to result from the reallocation of the resources used for building attractive flowers, as the need to attract pollinators decreases. 2,3 We investigated the similarities in the evolution of flower fragrance following independent transitions to self-fertilization in Capsella. 4,5,6,7,8,9 We identified several compounds that exhibited similar changes in different selfer lineages, such that the flower scent composition reflects mating systems rather than evolutionary history within this genus. We further demonstrate that the repeated loss of β -ocimene emission, one of the compounds most strongly affected by these transitions, was caused by mutations in different genes. In one of the Capsella selfing lineages, the loss of its emission was associated with a mutation altering subcellular localization of the ortholog of TERPENE SYNTHASE 2. This mutation appears to have been fixed early after the transition to selfing through the capture of variants segregating in the ancestral outcrossing population. The large extent of convergence in the independent evolution of flower scent, together with the evolutionary history and molecular consequences of a causal mutation, suggests that the emission of specific volatiles evolved as a response to changes in ecological pressures rather than resource limitation. [Display omitted] • Flower scent evolved similarly in the independent selfing lineages of Capsella • β -ocimene emission is highly reduced in both lineages • This reduction is attributed to distinct mutations in each selfing species • In C. rubella , it is linked to a decrease in chloroplastic levels of TPS02 Flower scent serves as chemical signals to attract pollinators in many plants. Wozniak et al. describe a very similar evolution of floral volatile emission after independent transitions to autogamy in the genus Capsella , emphasizing its ecological importance even when animal pollination is not required. [ABSTRACT FROM AUTHOR]

Banyan trees are distinguished by their extraordinary aerial roots. The Ficus genus includes species that have evolved a species-specific mutualism system with wasp pollinators. We sequenced genomes of the Chinese banyan tree, F. microcarpa , and a species lacking aerial roots, F. hispida, and one wasp genome coevolving with F. microcarpa , Eupristina verticillata. Comparative analysis of the two Ficus genomes revealed dynamic karyotype variation associated with adaptive evolution. Copy number expansion of auxin-related genes from duplications and elevated auxin production are associated with aerial root development in F. microcarpa. A male-specific AGAMOUS paralog, FhAG2 , was identified as a candidate gene for sex determination in F. hispida. Population genomic analyses of Ficus species revealed genomic signatures of morphological and physiological coadaptation with their pollinators involving terpenoid- and benzenoid-derived compounds. These three genomes offer insights into and genomic resources for investigating the geneses of aerial roots, monoecy and dioecy, and codiversification in a symbiotic system. • Genomes of two Ficus species and one wasp pollinator revealed fig-wasp coevolution • Aerial root formation is triggered by an auxin-dependent pathway promoted by light • A male-specific FhAG2 gene is a candidate gene for sex determination in F. hispida • Genes related to coadaptation contribute to codiversification between fig and wasp Comparative analyses of two Ficus genomes with and without aerial roots reveal insights into the genomic basis of aerial root formation and population genomic analyses of Ficus species alongside the genome of a coevolving wasp pollinator enhance our understanding of their species-specific mutualism. [ABSTRACT FROM AUTHOR]