The Responses of the Lipoxygenase Gene Family to Salt and Drought Stress in Foxtail Millet (Setaria italica)

Plant lipoxygenases (LOXs), a kind of non-heme iron-containing dioxygenases, participate plant physiological activities (especially in response to biotic and abiotic stresses) through oxidizing various lipids. However, there was few investigations on LOXs in foxtail millet (Setaria italica). In this study, we identified the LOX gene family in foxtail millet, and divided the total 12 members into three sub-families on the basis of their phylogenetic relationships. Under salt and drought stress, LOX genes showed different expression patterns. Among them, only SiLOX7 showed up-regulated expression in Yugu1 (YG1) and Qinhuang2 (QH2), two stress-tolerant varieties, indicating that SiLOX7 may play an important role in responses to abiotic stress. Our research provides a basis for further investigation of the role of LOX genes in the adaptation to abiotic stresses and other possible biological functions in foxtail millet.

Genome-wide identification and expression pattern analysis of lipoxygenase gene family in banana

The LOX genes have been identified and characterized in many plant species, but studies on the banana LOX genes are very limited. In this study, we respectively identified 18 MaLOX, 11 MbLOX, and 12 MiLOX genes from the Musa acuminata, M. balbisiana and M. itinerans genome data, investigated their gene structures and characterized the physicochemical properties of their encoded proteins. Banana LOXs showed a preference for using and ending with G/C and their encoded proteins can be classified into 9-LOX, Type I 13-LOX and Type II 13-LOX subfamilies. The expansion of the MaLOXs might result from the combined actions of genome-wide, tandem, and segmental duplications. However, tandem and segmental duplications contribute to the expansion of MbLOXs. Transcriptome data based gene expression analysis showed that MaLOX1, 4, and 7 were highly expressed in fruit and their expression levels were significantly regulated by ethylene. And 11, 12 and 7 MaLOXs were found to be low temperature-, high temperature-, and Fusarium oxysporum f. sp. Cubense tropical race 4 (FocTR4)-responsive, respectively. MaLOX8, 9 and 13 are responsive to all the three stresses, MaLOX4 and MaLOX12 are high temperature- and FocTR4-responsive; MaLOX6 and MaLOX17 are significantly induced by low temperature and FocTR4; and the expression of MaLOX7 and MaLOX16 are only affected by high temperature. Quantitative real-time PCR (qRT-PCR) analysis revealed that the expression levels of several MaLOXs are regulated by MeJA and FocTR4, indicating that they can increase the resistance of banana by regulating the JA pathway. Additionally, the weighted gene co-expression network analysis (WGCNA) of MaLOXs revealed 3 models respectively for 5 (MaLOX7-11), 3 (MaLOX6, 13, and 17), and 1 (MaLOX12) MaLOX genes. Our findings can provide valuable information for the characterization, evolution, diversity and functionality of MaLOX, MbLOX and MiLOX genes and are helpful for understanding the roles of LOXs in banana growth and development and adaptations to different stresses.

Identification, Phylogeny, and Comparative Expression of the Lipoxygenase Gene Family of the Aquatic Duckweed, Spirodela polyrhiza, during Growth and in Response to Methyl Jasmonate and Salt

Lipoxygenases (LOXs) (EC 1.13.11.12) catalyze the oxygenation of fatty acids and produce oxylipins, including the plant hormone jasmonic acid (JA) and its methyl ester, methyl jasmonate (MeJA). Little information is available about the LOX gene family in aquatic plants. We identified a novel LOX gene family comprising nine LOX genes in the aquatic plant Spirodela polyrhiza (greater duckweed). The reduced anatomy of S. polyrhiza did not lead to a reduction in LOX family genes. The 13-LOX subfamily, with seven genes, predominates, while the 9-LOX subfamily is reduced to two genes, an opposite trend from known LOX families of other plant species. As the 13-LOX subfamily is associated with the synthesis of JA/MeJA, its predominance in the Spirodela genome raises the possibility of a higher requirement for the hormone in the aquatic plant. JA-/MeJA-based feedback regulation during culture aging as well as the induction of LOX gene family members within 6 h of salt exposure are demonstrated.

Comprehensive Genomic Characterization and Expression Analysis of the Lipoxygenase Gene Family in Watermelon under Hormonal Treatments

Lipoxygenases (LOXs) are non-haem iron-containing dioxygenases and play vital roles in a variety of plant biological processes. Here, we first carried out the genome-wide identification of LOX genes in watermelon. A total of 16 LOX genes were identified, which could be classified into two categories according to phylogenetic analysis: the 9-LOXs (ClLOX1–4, 12, and 15) and 13-LOXs (ClLOX5–11, 13, 14, and 16). Furthermore, the protein structures, intrachromosomal distributions, and gene structures were thoroughly analyzed. Cis-element analysis of the promoter regions indicated that the expression of ClLOX genes may be influenced by stress and plant hormones. Bioinformatic and expression analyses revealed that the expression of ClLOX genes is tissue-specific and hormone-responsive. The detected LOX genes exhibited distinctive expression patterns in various tissues. Different ClLOX genes showed different responses to methyl jasmonate (MeJA), salicylic acid (SA), and ethylene (ET) treatments, particularly ClLOX7, which exhibited the most active response to the above treatments. This study provides valuable information for a better understanding of the functions of LOX genes and further exploration of the LOX gene family in watermelon.

Bioinformatics Analysis of the Lipoxygenase Gene Family in Radish (Raphanus sativus) and Functional Characterization in Response to Abiotic and Biotic Stresses

Lipoxygenases (LOXs) are non-heme iron-containing dioxygenases involved in many developmental and stress-responsive processes in plants. However, little is known about the radish LOX gene family members and their functions in response to biotic and abiotic stresses. In this study, we completed a genome-wide analysis and expression profiling of RsLOX genes under abiotic and biotic stress conditions. We identified 11 RsLOX genes, which encoded conserved domains, and classified them in 9-LOX and 13-LOX categories according to their phylogenetic relationships. The characteristic structural features of 9-LOX and 13-LOX genes and the encoded protein domains as well as their evolution are presented herein. A qRT-PCR analysis of RsLOX expression levels in the roots under simulated drought, salinity, heat, and cold stresses, as well as in response to a Plasmodiophora brassicae infection, revealed three tandem-clustered RsLOX genes that are involved in responses to various environmental stresses via the jasmonic acid pathway. Our findings provide insights into the evolution and potential biological roles of RsLOXs related to the adaptation of radish to stress conditions.