Academic journal article Genetics

An Epiallele at Cly1 Affects the Expression of Floret Closing (Cleistogamy) in Barley

Academic journal article Genetics

An Epiallele at Cly1 Affects the Expression of Floret Closing (Cleistogamy) in Barley

Article excerpt

ABSTRACT The swelling of the lodicule is responsible for floret opening in many grass species, allowing for pollen dispersal and cross-pollination. In barley, the closed floret habit (cleistogamy) is under the control of cly1, a gene that operates by inhibiting the development of the lodicule. In non-cleistogamous cultivars, cly1 mRNA is degraded by miR172-directed cleavage, allowing the lodicules to swell; however, in cultivars carrying the recessive allele cly1.b, a single-nucleotide substitution destroys the miR172 target site preventing mRNA cleavage. Barley cv. SV235 is cleistogamous; its cly1 coding sequence is identical to that of cly1.b, but its lodicules do develop, although insufficiently to produce a non-cleistogamous flower. In this cultivar, the downregulation of cly1 is unrelated to miR172-directed mRNA degradation, but rather is caused by an epiallele that represses transcription. Allelic relationships between known cly1 alleles were explored by the quantification of lodicule vascularization and an assessment of the response of the spike to the supply of exogenous auxin. The SV235 phenotype can be manipulated by a pre-anthesis application of 2,4-D, a feature that could be of interest in the context of hybrid barley grain production based on cleistogamy.

THE swelling of the lodicule, a structure found in the floret of many grass species and functionally related to the petal in the hermaphroditic angiosperm flower, drives apart the palea and lemma, thereby opening the floret so that it can release its pollen and be readily cross-pollinated (Briggs 1978). In barley, closed flowering (cleistogamous) variants are known. In some of these, the lodicule fails to swell (Kurauchi et al. 1994; Turuspekov et al. 2004; Honda et al. 2005; Wang et αi 2013). The cleistogamy 1 gene (cly1) has been shown to encode an AP2-protein and is a paralog of HvAP2-like in barley and Q in bread wheat (Simons et al. 2006; Nair et al. 2010; Simonov and Pshenichnikova 2012; Ning et al. 2013). In non-cleistogamous barleys, cly1 mRNA is cleaved by an miRNA, with the result that the abundance of full-length gene product remains at a low level. Two cleistogamy alleles are known, cly1.b and cly1.c; in both cases, cly1 mRNA is not cleaved by miRl 72, resulting in the failure of the lodicule to swell. Exceptionally, in cv. SV235, although its cly1 coding sequence is identical to that of cly1.b, its lodicules do swell at anthesis, although insufficiently to force open the floret. Here, we show the genetic and epigenetic basis of the unusual lodicule development seen in cv. SV235.

Materials and Methods

Plant materials

Grain of the barley cultivars SV002 (OUA008, "Sanalta"), SV223 (OUU059, "Tammi"), SV230 (OUU305, "Badajoy"), SV235 (OUU326, "France 1"), SV237 (OUU329, "Cygne"), SV241 (OUU351, "Plumage"), SV242 (OUU352, "Imperial"), and SV255 (OUU613, "Otello"), along with the Hordeum vulgare subsp. spontaneum accession OUH602 (the OU numbers relate to the Barley and Wild Plant Resource Center collection, http://www.rib.okayama-u.ac.jp/barley/index.html), was obtained from the Institute of Plant Science and Resources, Okayama University, Kurashiki, Japan. The SV numbers represent designators within a core collection designed to capture the global diversity of barley (Saisho et al. 2009; Nair et al. 2010). Grain of the cultivars "Azumamugi" (AZ), "Kanto Nakate Gold" (KNG), and "Golden Promise" (GP) were supplied by the NIAS Gene Bank, Tsukuba, Japan, that of "Satsuki Nijo" (SN) by K. Matsui (National Institute of Crop Sdence, Tsukuba, Japan), that of "Barke" (BAR) by N. Stein (Leibniz Institute of Plant Genetics and Crop Plant Research, Gatersleben, Germany), and that of "Morex" (MOR) by A. Kleinhofs (Department of Crop and Soil Sciences and School of Molecular Biosciences, Washington State University, Pullman, WA). Plants were sown during the fall in the field at Tsukuba, spaced 20 cm apart in rows separated from one another by 80 cm. …

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