Search

Cytochrome P450 monooxygenases (P450s) catalyze a great number of biochemical reactions and play vital roles in plant growth, development and secondary metabolism. As yet, the genome-scale investigation on P450s is still lacking in the model legume Medicago truncatula. In particular, whether and how many MtP450s are involved in drought and salt stresses for Medicago growth, development and yield remain unclear. In this study, a total of 346 MtP450 genes were identified and classified into 10 clans containing 48 families. Among them, sixty-one MtP450 genes pairs are tandem duplication events and 10 MtP450 genes are segmental duplication events. MtP450 genes within one family exhibit high conservation and specificity in intron–exon structure. Meanwhile, many Mt450 genes displayed tissue-specific expression pattern in various tissues. Specifically, the expression pattern of 204 Mt450 genes under drought/NaCl treatments were analyzed by using the weighted correlation network analysis (WGCNA). Among them, eight genes (CYP72A59v1, CYP74B4, CYP71AU56, CYP81E9, CYP71A31, CYP704G6, CYP76Y14, and CYP78A126), and six genes (CYP83D3, CYP76F70, CYP72A66, CYP76E1, CYP74C12, and CYP94A52) were found to be hub genes under drought/NaCl treatments, respectively. The expression levels of these selected hub genes could be induced, respectively, by drought/NaCl treatments, as validated by qPCR analyses, and most of these genes are involved in the secondary metabolism and fatty acid pathways. The genome-wide identification and co-expression analyses of M. truncatulaP450 superfamily genes established a gene atlas for a deep and systematic investigation of P450 genes in M. truncatula, and the selected drought-/salt-responsive genes could be utilized for further functional characterization and molecular breeding for resistance in legume crops.

Legume plants are rich in prenylated flavonoid compounds, which play an important role in plant defense and human health. In the present study, we identified a prenyltransferase (PT) gene, named LaPT2, in white lupin (Lupinus albus), which shows a high identity and close relationship with the other known PT genes involved in flavonoid prenylation in planta. The recombinant LaPT2 protein expressed in yeast cells exhibited a relatively strong activity toward several flavonols (e.g., kaempferol, quercetin, and myricetin) and a relatively weak activity toward flavanone (naringenin). In addition, the recombinant LaPT2 protein was also active toward several other types of flavonoids, including galangin, morin, 5-deoxyquercetin, 4'-O-methylkaempferol, taxifolin, and aromadendrin, with distinct enzymatic affinities. The LaPT2 gene was preferentially expressed in the roots, which is consistent with the presence of prenylated flavonoid kaempferol in the roots. Moreover, we found that the expression level of LaPT2 paralleled with those of LaF3H1 and LaFLS2 genes that were relatively higher in roots and lower in leaves, suggesting that they were essential for the accumulation of prenylated flavonoid kaempferol in roots. The deduced full-length LaPT2 protein and its signal peptide fused with a green fluorescent protein (GFP) are targeted to plastids in the Arabidopsis thaliana protoplast. Our study demonstrated that LaPT2 from white lupin is responsible for the biosynthesis of prenylated flavonoids, in particular flavonols, which could be utilized as phytoalexin for plant defense and bioactive flavonoid compounds for human health.

Main Conclusion GbMYBR1, a new type of R2R3-MYB repressor from Ginkgo biloba, displayed pleiotropic effects on plant growth, phenylpropanoid accumulation, by regulating multiple related genes at different levels. Abstract Ginkgo biloba is a typical gymnosperm that has been thriving on earth for millions of years. MYB transcription factors (TFs) play important roles in diverse processes in plants. However, the role of MYBs remains largely unknown in Ginkgo. Here, an MYB TF gene from Ginkgo, designated as GbMYBR1, was found to act as a repressor in multiple processes. GbMYBR1 was mainly expressed in the leaves of Ginkgo. Over-expression of GbMYBR1 in Arabidopsis thaliana led to growth retardation, decreases in lignin content, reduced trichome density, and remarkable reduction in anthocyanin and flavonol contents in leaves. Proanthocyanidin content was decreased in the seeds of transgenic Arabidopsis, which led to light-brown seed color. Both qPCR and transcriptome sequencing analyses demonstrated that the transcript levels of multiple genes related to phenylpropanoid biosynthesis, trichome formation, and pathogen resistance were down-regulated in the transgenic Arabidopsis. In particular, we found that GbMYBR1 directly interacts with the bHLH cofactor GL3 as revealed by yeast two-hybrid assays. Our work indicated that GbMYBR1 has pleiotropic effects on plant growth, phenylpropanoid accumulation, and trichome development, mediated by interaction with GL3 or direct suppression of key pathway genes. Thus, GbMYBR1 represents a novel type of R2R3 MYB repressor.

Prenylated isoflavonoids have been found in several legume plants, and they possess various biological activities that play important roles in both plant defense and human health. However, it is still unknown whether prenylated isoflavonoids are present in the model legume plant Lotus japonicus. In the present study, we found that the prenylated isoflavonoid wighteone was produced in L. japonicus when leaf was supplemented with genistein. Furthermore, a novel prenyltransferase gene, LjG6DT, was identified, which shared high similarity with and was closely related to several known prenyltransferase genes involved in isoflavonoid biosynthesis. The recombinant LjG6DT protein expressed in yeast exhibited prenylation activity toward genistein as an exclusive substrate, which produced wighteone, a prenylated genistein at the C-6 position that occurs normally in legume plants. The LjG6DT-green fluorescent protein (GFP) fusion protein is targeted to plastids. The transcript level of LjG6DT is induced by glutathione, methyl jasmonate and salicylic acid, implying that LjG6DT is involved in stress response. Overexpression of LjG6DT in L. japonicus hairy roots led to increased accumulation of wighteone when genistein was supplied, indicating that LjG6DT is functional in vivo. Feeding assays with the upstream intermediate naringenin revealed that accumulation of wighteone in L. japonicus was dependent on genistein supplementation, and accumulation of wighteone is competed by genistein methylation. This study demonstrated that phytoalexin wighteone is inducibly produced in L. japonicus, and it provides new insight into the biosynthesis and accumulation of prenylated isoflavonoids in legume plants.