RH17 restricts reproductive fate and represses autonomous seed coat development in sexual Arabidopsis

Abstract

Plant sexual and asexual reproduction through seeds (apomixis) is tightly controlled by complex gene regulatory programs. These are to date not fully understood. Recent findings suggest that RNA helicases are required for plant germline development. This resembles their crucial roles in animals, where they are involved in controlling gene activity and the maintenance of genome integrity. Here we identified novel roles of Arabidopsis RH17 during reproductive development. Interestingly, RH17 is involved in repression of reproductive fate and of elements of seed development in the absence of fertilization. In lines carrying a mutant rh17 allele, development of supernumerary reproductive cell lineages in the female flower tissues (ovules) was observed, occasionally leading to formation of two embryos per seed. Furthermore, seed coat and putatively also endosperm development frequently initiated autonomously. Such induction of several features phenocopying distinct elements of apomixis by a single mutation is rather exceptional and suggests that RH17 acts in regulatory control of plant reproductive development. In longer terms, an in depth understanding of its action might provide a basis for harnessing for agricultural applications.

Differential expression analysis of sexual and apomicticBoecherauncoversFAS4as crucial for gametogenesis

“…Per sample, between 99 and 223 sections of nucellus tissue were pooled (Table S1). Isolation of mature ovules and subsequent RNA isolation followed protocols previously described for A. thaliana (Stein et al, 2021) (Supporting Information). Library preparation from samples isolated by LAM was done with NEB Ultra II FS gDNA library preparation kit.…”

“…To investigate female gametophyte development in the A. thaliana lines carrying mutant alleles of FAS4 as compared to the wild-type, ovule clearing and microscopy were performed as described previously (Stein et al, 2021) (Supporting Information), unlike that for AtFAS4genomic-PmTurquoise or BsFAS4orth genomic-mVenus lines imaging were acquired sequentially with a Zeiss LSM710 microscope. (Kiefer et al, 2019).…”

“…Interestingly, in A. thaliana both are essential for seed development (Meinke, 2020, Pagnussat et al, 2005). In addition, plants carrying mutant alleles of MNEME or RH17 show features of apomixis (Stein et al, 2021, Schmidt et al, 2011).…”

Overcoming roadblocks for in vitro nurseries in plants: induction of meiosis

“…KRP4, KRP6, and KRP 7 (KIP-RELATED PROTEIN 4,5,6) as well as RETINOBLASTOMA RELATED1 (RBR1), prevent the formation of supernumerary meiocytes from forming next to an already existing meiocyte while the repression of WUSCHEL (WUS) by RBR1 allows entry into meiosis (Zhao et al, 2017). An RNAhelicase (RH17) was found to play a role in reproduction as supernumerary reproductive cell lineages developed at a rate of over 20% in lines that were heterozygous for an rh17 mutant allele (Stein et al, 2021). Evidence for potential clues in phase change induction is further supported by the Mitosis instead of Meiosis phenotype in rice and Arabidopsis, where mutations in only three genes prevent meiotic cell entry and instead meiocytes in the A schematic comparison of germline development in humans vs. plants.…”