Expression and functional analysis of the barley Nud gene using transgenic rice

Abstract

Most cereal crops have hulless grains (naked caryopses) with a free-threshing trait, whereas the majority of barley cultivars show hulled (covered) caryopses. The naked caryopsis in barley is genetically controlled by a single locus, nud. The Nud gene (the covered caryopsis allele) encodes an ethylene response factor (ERF) family transcription factor that regulates a lipid biosynthetic pathway. For functional analysis of the barley Nud gene, we produced transgenic rice expressing Nud in the developing caryopses. All transgenic lines had caryopses that were easily dehulled at maturity, indicating that the naked caryopsis phenotype remained in spite of expression of the Nud transgene. Histochemical and lipid analyses of the transgenic rice caryopses did not show increased lipid accumulation on the surface of developing caryopses, suggesting that the Nudmediated lipid pathway may not function in rice caryopses. The predicted rice ortholog of Nud, Os06ERF was expressed specifically in the developing caryopses. However, expression of Os06ERF ceased at an earlier developmental stage than that of the native Nud gene in barley caryopses, which was also the case for expression of the Nud transgene. This raises the alternative hypothesis that the timing of Nud expression may be critical for activating the pathway for hull-caryopsis adhesion.

Husk to caryopsis adhesion in barley is influenced by pre- and post-anthesis temperatures through changes in a cuticular cementing layer on the caryopsis

“…The composition of the surface lipids of the barley caryopsis has not yet been reported. However, Kakeda et al [ 65 ] compared thin-layer chromatographs of surface lipids extracted from the caryopses of covered and naked barley, and found little evidence of solvent-extractable compounds being present on the naked barley caryopses, despite there being a thin cuticle present on naked barley caryopses. With the findings of Taketa et al [ 18 ] that the cementing material could be dyed by Sudan Black dye, this indicates that the cementing material itself is likely to be extractable using organic solvents.…”

Development and Quality of Barley Husk Adhesion Correlates With Changes in Caryopsis Cuticle Biosynthesis and Composition

“…The study of Duan et al (2015) utilized two barley cultivars from very different genetic backgrounds, therefore it is possible that other regulatory elements could be responsible for the observed differences. Although NUD may determine the covered or naked phenotype through causing changes in cementing layer development or composition (Taketa et al, 2008; Kakeda et al, 2011), there is no evidence among covered cultivars, that the observed differences in adhesion quality are regulated by NUD in the same way.…”

The Structure of the Barley Husk Influences Its Resistance to Mechanical Stress

“…This is significant, as increased cuticle permeability has been implicated in adhesion or organ fusion in a range of plant species (Yephremov et al, 1999 ; Sieber et al, 2000 ; Smirnova et al, 2013 ; Yeats and Rose, 2013 ). A functional NUD gene, which encodes an ethylene responsive transcription factor, is necessary, although not sufficient, for the development of the cementing layer and a permeable pericarp cuticle (Taketa et al, 2008 ; Kakeda et al, 2011 ). Without these modifications to the pericarp cuticle, there can be no adhesion between the barley caryopsis and the barley husk, or the adhesion is critically impaired in some way.…”