Abstract
Main conclusionAustralian native species of sorghum contain negligible amounts of dhurrin in their leaves and the cyanogenesis process is regulated differently under water-stress in comparison to domesticated sorghum species.Cyanogenesis in forage sorghum is a major concern in agriculture as the leaves of domesticated sorghum are potentially toxic to livestock, especially at times of drought which induces increased production of the cyanogenic glucoside dhurrin. The wild sorghum species endemic to Australia have a negligible content of dhurrin in the above ground tissues and thus represent a potential resource for key agricultural traits like low toxicity. In this study we investigated the differential expression of cyanogenesis related genes in the leaf tissue of the domesticated species Sorghum bicolor and the Australian native wild species Sorghum macrospermum grown in glasshouse-controlled water-stress conditions using RNA-Seq analysis to analyse gene expression. The study identified genes, including those in the cyanogenesis pathway, that were differentially regulated in response to water-stress in domesticated and wild sorghum. In the domesticated sorghum, dhurrin content was significantly higher compared to that in the wild sorghum and increased with stress and decreased with age whereas in wild sorghum the dhurrin content remained negligible. The key genes in dhurrin biosynthesis, CYP79A1, CYP71E1 and UGT85B1, were shown to be highly expressed in S. bicolor. DHR and HNL encoding the dhurrinase and α-hydroxynitrilase catalysing bio-activation of dhurrin were also highly expressed in S. bicolor. Analysis of the differences in expression of cyanogenesis related genes between domesticated and wild sorghum species may allow the use of these genetic resources to produce more acyanogenic varieties in the future.
Highlights
Water-stress is a key abiotic stress factor in crop production causing reduced yields (Farooq et al 2009) and inducing vastly altered expression profiles for genes related to plant growth and development (Takahashi et al 2018; Luo et al 2014; Shankar et al 2013; Ahuja et al 2010)
The differential gene expression of S. bicolor in response to water-stress has been investigated in several studies (Abdel-Ghany et al 2020; Johnson et al 2014; Dugas et al 2011) and has identified many up-regulated and down-regulated genes encoding formation of protective molecules and regulatory factors such as dehydrins (DHN), aquaporins (AQP), abscisic acid (ABA) responsive proteins, drought-responsive element binding proteins (DREB), cryoprotectants, detoxification related genes, osmoprotectants as well as membrane composition and signalling molecules (Abdel-Ghany et al 2020; AzzouzOlden et al 2020; Gosal et al 2009; Fetter et al 2004)
In the present study we demonstrate that, even under severe stress, S. bicolor leaves have around a 1000-fold higher Hydrogen cyanide potential (HCNp) than the wild sorghums
Summary
Water-stress is a key abiotic stress factor in crop production causing reduced yields (Farooq et al 2009) and inducing vastly altered expression profiles for genes related to plant growth and development (Takahashi et al 2018; Luo et al 2014; Shankar et al 2013; Ahuja et al 2010). The differential gene expression of S. bicolor in response to water-stress has been investigated in several studies (Abdel-Ghany et al 2020; Johnson et al 2014; Dugas et al 2011) and has identified many up-regulated and down-regulated genes encoding formation of protective molecules and regulatory factors such as dehydrins (DHN), aquaporins (AQP), abscisic acid (ABA) responsive proteins, drought-responsive element binding proteins (DREB), cryoprotectants, detoxification related genes, osmoprotectants as well as membrane composition and signalling molecules (Abdel-Ghany et al 2020; AzzouzOlden et al 2020; Gosal et al 2009; Fetter et al 2004). Cyanogenic glycosides are amino acid derived bioactive compounds identified in more than 3000 plant species (Gleadow and Moller 2014). In addition to sorghum (Kojima et al 1979), species such as almonds (Sánchez-Pérez et al 2019), cassava (Jorgensen et al 2005), macadamia nuts (Dahler et al 1995) and barley (Knoch et al 2016) produce cyanogenic glycosides
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