An Epiallele at cly1 Affects the Expression of Floret Closing (Cleistogamy) in Barley

Abstract

The swelling of the lodicule is responsible for floret opening in many grass species, allowing for pollen dispersal and crosspollination. 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.T HE 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 al. 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 noncleistogamous 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 miR172, 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 materialsGrain 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...

Increase of DNA Methylation at the HvCKX2.1 Promoter by Terminal Drought Stress in Barley

“…During early seedling development, the regulation mediated by the presence of miR165, miR166, miR164 and miR319 is of special importance for germination and developmental phase transitions [9,10]. In barley, miR172 was identified as a regulator of floret closing [11] and the density of grains [12]. Recently, the function of several miRNAs in response to abiotic stimuli, especially as drought stress response, was also further elucidated [13].…”

Cleistogamy and phylogenetic position ofViola uliginosa(Violaceae) re-examined

“…The genetic basis of cleistogamy is still poorly understood although it has attracted considerable attention in recent years because CL genotypes of important crops, such as rice, barley, rape and soya (Turuspekov et al ., ; Maeng et al ., ; Yoshida et al ., ; Leflon et al ., , ; Wang et al ., ) or important medicinal plants, such as Catharanthus roseus (L.) G.Don (Kulkarni & Baskaran, ), could maintain genetic purity and seed production independent of pollinators by cleistogamy. Less is known about the genes involved in cleistogamy in violets.…”

“…This mixed reproductive system, especially induction of CL flowers in economically important crops, is of great interest as a possible alternative to apomixis in the production of genetically uniform selected lines. The molecular mechanisms of cleistogamy remain largely unknown, with several papers published in the last few years (Turuspekov et al ., ; Wang, ; Wang et al ., ).…”

Grass flowers: An untapped resource for floral evo‐devo

“…This change in transcript regulation results in lodicules that are much smaller than those seen in wild type, and in cleistogamy, in which flowers are unable to open, enabling self‐pollination rather than outcrossing (Kuusk et al, ). A CLY1 epiallele with altered transcript level not associated with sequence variation at the miR172 binding site resulted in lodicules that were able to swell, although not enough to push the flower open (Wang et al, ). AP2‐ like genes in all three genomes of hexaploid wheat, the TaAP2/WAP2 homeologs, are each also regulated by miR172.…”