Molecular Mechanisms Underlying Hull-Caryopsis Adhesion/Separation Revealed by Comparative Transcriptomic Analysis of Covered/Naked Barley (Hordeum vulgare L.)

Abstract

The covered/naked caryopsis trait of barley is an important agronomic trait because it is directly linked to dietary use. The formation of covered/naked caryopsis is controlled by an NUD transcription factor, which is involved in pericarp cuticle development. However, the molecular mechanism underlying this trait remains so far largely unknown. In this study, comparative transcriptomes of grains three weeks after anthesis of Tibetan Hulless barley landrace Dulihuang and covered barley Morex were analyzed using RNA-seq technique. A total of 4031 differentially expressed genes (DEGs) were identified. The Nud gene was overexpressed in Morex, with trace expression in Dulihuang. Among seventeen cuticle related DEGs, sixteen were down regulated and one up regulated in Morex. These results suggest that the Nud gene in covered caryopsis might down regulate cuticle related genes, which may cause a permeable cuticle over pericarp, leading to a hull-caryopsis organ fusion. A functional cuticle covering the pericarp of naked caryopsis might be the result of deletion or low expression level of the Nud gene. The functional cuticle defines a perfect boundary to separate the caryopsis from the hull in naked barley.

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

“…Organ fusion has been induced by expression of a fungal cutinase in Arabidopsis , where cuticular layers either remaned intact between cell walls, or walls of epidermal cells came in direct contact with each other [ 71 ]; organ fusion has also been induced by repression of WIN1/SHN1 , a gene with homology to Nud , in Arabidopsis and Tourenia fournieri [ 72 ]. The increase in abundance of compounds known to increase cuticle permeability in samples with the highest quality husk adhesion, supports the observations of Duan et al [ 43 ] that the process of husk adhesion is similar to organ fusion, and may be due to an increase in cuticle permeability. Although the present study suggests that cuticular wax composition has a role in the quality of husk adhesion, it is possible that the entire matrix of cell-wall, cutin and cuticular waxes contribute to husk adhesion.…”

“…The long-chain alkane tritriacontane was also associated with good quality husk adhesion; n -alkanes have also been linked to cuticular permeability [ 66 ], however in tomato fruits, higher-chain alkanes with C 31 to C 34 were associated with lower cuticle permeability [ 67 ]. Organ fusion has been previously noted to be a similar phenotype to husk adhesion [ 43 ]. In the maize ad1 mutant, where the cell walls of floral parts adhere to each other, the cuticle appears to remain intact between the cell walls [ 41 ], similar in appearance to the cementing layer comprising the husk and pericarp surface cuticles.…”

“…Cuticle properties such as transpiration rate and permeability, are more highly influenced by their composition rather than by the thickness of the cuticle, or amount of wax. Indeed, mutations in several cuticle-synthesis associated genes alter cuticle permeability, and display an organ fusion phenotype [ 38 – 42 ], which has similarity to the process of husk adhesion, in that adjacent organs adhere to one another through the cuticle [ 18 , 43 ].…”

Variation in grain skinning among spring barley varieties induced by a controlled environment misting screen

“…The covered/ naked phenotype is determined by expression of the Nud gene, which is typically deleted in naked barleys (Taketa et al 2008). However a recent study has shown that Nud is expressed at low levels in some Tibetan naked barley cultivars (Duan et al 2015), therefore differences in the quality of husk adhesion observed among these barley varieties may in fact be regulated by differential expression of Nud under the misting treatment. The misting treatment significantly increased the proportion of skinned grains without having an effect on ear length, floret number, grain number or grain weight.…”

Comparative de novo transcriptome analysis of barley varieties with different malting qualities

“…The study of the transcriptome of an organism is one of the most effective ways to investigate the structure and function of its active genes (Gutierrez-Gonzales et al 2013 ). Comparative analyses of transcriptomes using RNA-Seq techniques were performed by Duan et al ( 2015 ) to study the formation of covered/naked caryopsis in Tibetan hulless barley landrace Dulihuang and covered barley Morex. They identified 4031 differentially expressed genes (DEGs) in total and proposed Myb regulation of wax biosynthesis pathway to be involved in naked caryopsis.…”