Maruthachalam, R. | Search bioRxiv

bioRxiv2023

Gametophytic epigenetic regulators MEA and DME synergistically suppress ectopic shoot formation in Arabidopsis

The gametophyte to sporophyte transition facilitates the alternation of generations in a plant life cycle. The epigenetic regulators DEMETER(DME) and MEDEA(MEA) synergistically control central cell proliferation and differentiation, ensuring proper gametophyte to sporo-phyte transition in Arabidopsis. Mutant alleles of DME and MEA are female gametophyte lethal, eluding the recovery of recessive homozygotes to examine their role in the sporophyte. Here, we exploited the paternal transmission of these mutant alleles coupled with CENH3-haploid inducer to generate mea-1;dme-2 sporophytes. Strikingly, the simultaneous loss of function of MEA and DME leads to the emergence of ectopic shoot meristems at the apical pole of the plant body axis. DME and MEA are expressed in the developing shoot apex and regulate the expression of various shoot-promoting factors. Chromatin immunoprecipitation(ChIP), DNA methylation and gene expression analysis revealed several shoot regulators as potential targets of MEA and DME. Knockdown of upregulated shoot-promoting factors STM, CUC2, and PLT5 rescued the ectopic shoot phenotypes. Our findings reveal a previously unrecognized synergistic role of MEA and DME in restricting the meristematic activity at the shoot apex during sporophytic development to orchestrate the plant architecture.

plant biology↗

bioRxiv2021

Biased removal and loading of centromeric histone H3 during reproduction underlies uniparental genome elimination

Uniparental genome elimination is a dramatic case of centromeric failure, resulting in the postzygotic loss of a parental chromosome set. Genome partitioning during cell division relies on centromere attachment to spindle fibers through kinetochores. Centromeres are epigenetically specified by CENP-A (CENH3), a conserved centromeric specific histone H3 variant. In Arabidopsis, CENH3 modification results in haploid inducers, whose genome is eliminated frequently when crossed to the wild type. To investigate the underlying mechanism, we dissected the timing and molecular features of genome elimination. In zygotes and early embryos from genome elimination crosses, CENH3 occupied only the centromeres contributed by the wild-type parent. Haploid inducer chromosomes had defective kinetochores and missegregated, often forming micronuclei. This uniparental loss of centromere identity is initiated by the removal of altered CENH3 at fertilization, while wild-type CENH3 persists and maintains strong centromeric identity. Weak centromeres were capable of rebuilding functional kinetochores, but often failed when in competition with normal ones. We induced a similar weak state by mitotic dilution of wild-type CENH3. Furthermore, weakness was suppressed by crosses of haploid inducers to other variants of haploid inducers, and enhanced by mutations in VIM1, a ubiquitin ligase known to modify CENH3 and centromeric DNA methylation.. The differential stability of altered CENH3 during reproduction has important genetic and evolutionary implications.

cell biology↗