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. 2018 Dec 20;11(1):ply076.
doi: 10.1093/aobpla/ply076. eCollection 2019 Feb.

Identification and expression of genes associated with the abscission layer controlling seed shattering in Lolium perenne

Zeyu Fu  1 , Jiancheng Song  1   2 , Jiqiang Zhao  2 , Paula E Jameson  1
Affiliations

Identification and expression of genes associated with the abscission layer controlling seed shattering in Lolium perenne

Zeyu Fu et al. AoB Plants. .

Abstract

Perennial ryegrass (Lolium perenne) is one of the most important pasture grasses in the world. However, seed production is negatively impacted by the seed shattering (shedding) nature of this species. Recently, genes involved in the seed shattering process have been isolated and functionally characterized in several crop species. The aim of this study was to identify the genes playing critical roles in the seed shattering process in perennial ryegrass. DNA sequences of genes involved in seed shattering in the Poaceae were used to identify and isolate target genes in perennial ryegrass using a comparative genomics strategy. The candidate seed shattering genes were identified using an 'in-house' perennial ryegrass transcriptome database. The relative expression levels of the candidate ryegrass shattering genes were determined using RT-qPCR during different floret and seed developmental stages. Histological analysis of the abscission layer was also conducted. Homologues of seed shattering genes were identified and isolated from perennial ryegrass, and the relative gene expression results suggested that several genes, including LpqSH1 and LpSH1, might have a role in abscission layer formation during seed development. In addition, lignification of the abscission layer may play an important role in the abscission process. A genetic model for seed shattering in perennial ryegrass is suggested and may be useful for directing gene editing towards the production of a reduced-shattering ryegrass.

Keywords: Abscission layer; LpSH1; RT–qPCR; comparative genomics; gene expression; lignification; perennial ryegrass; seed shattering.

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Figures

Figure 1.
Figure 1.
Rooted phylogenetic tree of candidate target seed shattering homologues in monocots. All homologues from perennial ryegrass are marked [·]. The phylogenetic tree was rooted using a Ginkgo AP2 sequence. Each homologue was renamed for easy reference. Refer also to Supporting Information—Table S1 for accession numbers. Ta, Triticum aestivum; Os, Oryza sativa; Lp, Lolium perenne; Or, Oryza rufipogon; Pe, Phyllostachys edulis; Hv, Hordeum vulgare; Sb, Sorghum bicolor; Zm, Zea mays; Sv, Sorghum virgatum; Si, Setaria italic; Bd, Brachypodium distachyon; Ec, Echinochloa crus-pavonis.
Figure 2.
Figure 2.
Relative expression of putative seed shattering genes. LpqSH1, LpSH5, LpSH4, LpSHAT1, LpSH1. LpLG1, LpWRKY and LpQ in perennial ryegrass cv. RI009 (first biological replicate). The plant material was collected from the glasshouse at the University of Canterbury, New Zealand, from October to December in 2014. Values are the mean of three technical replicates (±SD).
Figure 3.
Figure 3.
The overall pattern of relative expression levels of candidate seed shattering genes LpqSH1, LpSH5, LpSH4, LpSHAT1, LpSH1 LpLG1, LpWRKY and LpQ from perennial ryegrass cv. Nui (third biological replicate). The plant material was collected from field plots at Yantai University campus, China, from May to June in 2015. The relative expression levels are calculated relative to the lowest expressed sample within the same experiment.
Figure 4.
Figure 4.
Gene structure of LpSH1.
Figure 5.
Figure 5.
Amino acid sequence alignment of LpSH1 and its homologous proteins. A zinc-finger domain is indicated with the shaded box. The YABBY domain is underlined and in bold for LpSH1. The protein accessions are as follow, HvYABBY2 (Hordeum vulgare, BAJ89435.1); SiYABBY2 (Setaria italica, XP_004982272.1); ObYABBY2 (Oryza brachyantha, XP_006650352.1); TaYABBY2 (Triticum aestivum, ABW80974.1); OsYABBY2 (Oryza sativa, XP_015628574.1); ZmYABBY2 (Zea mays, XP_008666788.2).
Figure 6.
Figure 6.
Morphological and histological analysis of the abscission layer at the base of the seed within part of a spikelet. (A) Mature seed on spikelet of perennial ryegrass cv. Med line 1. (B) Enlarged images of the boxed area in (A), showing abscission layer located below the seed, indicated by the blue arrow. (C) Histological longitudinal sections of mature seed on a spikelet collected at 24 days after anthesis. Abscission layers are indicated by arrows.
Figure 7.
Figure 7.
Histological analysis of abscission layer. (A–F) Images of longitudinal sections across the abscission layer at 0 (A and D), 14 (B and E), 24 (C and F) days after anthesis for perennial ryegrass cv. Arrow (A–C) and cv. Med line 1 (D–F), respectively. Sections were stained with safranin-fast green, and the abscission layer is indicated by arrows.
Figure 8.
Figure 8.
Genetic model for seed shattering in perennial ryegrass.
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