Natural Variation in Ovule Morphology Is Influenced by Multiple Tissues and Impacts Downstream Grain Development in Barley (Hordeum vulgare L.)

Abstract

The ovule plays a critical role in cereal yield as it is the site of fertilization and the progenitor of the grain. The ovule primordium is generally comprised of three domains, the funiculus, chalaza, and nucellus, which give rise to distinct tissues including the integuments, nucellar projection, and embryo sac. The size and arrangement of these domains varies significantly between model eudicots, such as Arabidopsis thaliana, and agriculturally important monocotyledonous cereal species, such as Hordeum vulgare (barley). However, the amount of variation in ovule development among genotypes of a single species, and its functional significance, remains unclear. To address this, wholemount clearing was used to examine the details of ovule development in barley. Nine sporophytic and gametophytic features were examined at ovule maturity in a panel of 150 European two-row spring barley genotypes, and compared with grain traits from the preceding and same generation. Correlations were identified between ovule traits and features of grain they produced, which in general highlighted a negative correlation between nucellus area, ovule area, and grain weight. We speculate that the amount of ovule tissue, particularly the size of the nucellus, may affect the timing of maternal resource allocation to the fertilized embryo sac, thereby influencing subsequent grain development.

Ovule cell wall composition is a maternal determinant of grain size in barley

“…CC-BY-NC-ND 4.0 International license perpetuity. It is made available under a preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in The copyright holder for this this version posted December 3, 2022. ; https://doi.org/10.1101/2022.12.02.518939 doi: bioRxiv preprint strong positive correlation with ovule area, ovule length and ovule width (Wilkinson et al, 2019). Here we provide further support for this relationship by removing PME activity, a negative regulator of nucellus growth, which results in increased ovule length and width.…”

“…(p-r) Histone H4 in situ hybridization in opm1 opm2 ovules at the same stage as (j-l). Considering the nucellus occupies a large proportion of the whole ovule (Wilkinson et al, 2019), we investigated if changes in HG accumulation due to reduced PME activity affected ovule size, ovary size and grain size. In both the opm1 opm2 mutant and pMADS31::PMEI-eGFP transgenic plants, ovule length was increased while ovule width remained similar compared to wild-type (Fig.…”

HvLEAFY controls the early stages of floral organ specification and inhibits the formation of multiple ovaries in barley

“…To address possible defects in mov5.o ovule tissue identity and embryo sac development, immunolabelling was performed on transverse sections of mature wild-type and mov5.o carpels using antibodies that recognize prominent ovule cell wall epitopes: (1,3;1,4)-b-Dglucan and de-methylesterified pectin (Tucker et al, 2018) (Figure S3). In ovules from wild-type plants (stage Ov10), (1,3;1,4)-b-D-glucan was detected in the inner and outer integuments, as well as in the nucellus cells adjacent to the embryo sac (Figure S3d) (Wilkinson et al, 2019). Demethylesterified pectin was predominantly distributed in the nucellus cells surrounding the embryo sac, in a pattern that partially overlaps with (1,3;1,4)-b-D-glucan labelling (Figure S3d).…”

GWAS reveals the genetic complexity of fructan accumulation patterns in barley grain

“…Raw expression data were mapped against the transcriptome of barley (https://webblast.ipk-gatersleben.de/barley_ibsc/downloads/; merging high-confidence and low-confidence transcripts as well as isoforms) using Salmon v14.0 (Patro et al , 2007). RNA-sequencing data were obtained from developing pistils at Waddington (W) stages W8, W8.5, W9, W9.5 and W10 (Wilkinson et al ., 2019) and are shown as a mean value for five genotypes including Golden Promise (1x replicate per stage; Aubert et al ., 2018), Salka, Wren, Forum and Gant (2x replicates per stage). In addition, RNA-sequencing data from individual pistil tissues including the nucellus, integuments, ovary wall, embryo sac, egg apparatus and central cell, antipodal cells, and chalaza were analysed from the Sloop genotype.…”