Abstract
Lipoxygenases (LOXs) are a gene family of nonheme iron-containing dioxygenases that play important roles in plant development and defense responses. To date, a comprehensive analysis of LOX genes and their biological functions in response to abiotic stresses in peanut has not been performed. In this study, a total of 72 putative LOX genes were identified in cultivated (Arachis hypogaea) and wild-type peanut (Arachis duranensis and Arachis ipaensis) and classified into three subfamilies: 9-LOX, type I 13-LOX and type II 13-LOX. The gene structures and protein motifs of these peanut LOX genes were highly conserved among most LOXs. We found that the chromosomal distribution of peanut LOXs was not random and that gene duplication played a crucial role in the expansion of the LOX gene family. Cis-acting elements related to development, hormones, and biotic and abiotic stresses were identified in the promoters of peanut LOX genes. The expression patterns of peanut LOX genes were tissue-specific and stress-inducible. Quantitative real-time PCR results further confirmed that peanut LOX gene expression could be induced by drought, salt, methyl jasmonate and abscisic acid treatments, and these genes exhibited diverse expression patterns. Furthermore, overexpression of AhLOX29 in Arabidopsis enhanced the resistance to drought stress. Compared with wide-type, AhLOX29-overexpressing plants showed significantly decreased malondialdehyde contents, as well as increased chlorophyll degradation, proline accumulation and superoxide dismutase activity, suggesting that the transgenic plants exhibit strengthened capacity to scavenge reactive oxygen species and prevent membrane damage. This systematic study provides valuable information about the functional characteristics of AhLOXs in the regulation of abiotic stress responses of peanut.
Highlights
Peanut is one of the most important economic crops producing healthy oil and high-quality protein for global human diets (Bertioli et al, 2016)
Based on the analysis of physical and chemical properties, we found that the length of peanut LOX proteins ranged between 509 (AdLOX5) and 1,491 amino acids (AhLOX25), and the molecular weight of LOX proteins ranged from 58.35 kDa (AdLOX5) to 170.64 kDa (AhLOX25)
The classification and phylogenetics of LOX proteins have been analyzed in several plants, such as Arabidopsis, Glycine max, and Medicago truncatula (Jin et al, 2008; Umate, 2011; Ogunola et al, 2017), helping us to classify the evolutionary relationships of the peanut LOX proteins
Summary
Peanut is one of the most important economic crops producing healthy oil and high-quality protein for global human diets (Bertioli et al, 2016). The synthesis of oxylipins and their derivatives, such as jasmonic acid (JA), green leaf volatiles, divinyl ethers and traumatic acid, is catalyzed by LOXs in the LOX pathway (Silke and Baldwin, 2010; Christensen et al, 2015). These oxylipins have been evidenced to be involved in plant responses to various stresses (Porta and Rocha-Sosa, 2002; Zhou et al, 2009). In the LOX metabolic pathway, LOXs catalyze polyunsaturated fatty acids, such as LA, α-LeA and arachidonic acid, to produce either 13S- or 9S-hydroperoxy derivatives (Feussner and Wasternack, 2002) These hydroperoxides are metabolized via several secondary reactions and converted into diverse oxylipins. More recent studies have focused on the functions of plant LOXs, especially with regard to growth, development, and stress responses
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