BackgroundWood basic density (WBD), the biomass of plant cell walls per unit volume, is an important trait for elite tree selection in kraft pulp production. Here, we investigated the correlation between WBD and wood volumes or wood properties using 98 open-pollinated, 2.4 to 2.8 year-old hybrid Eucalyptus (Eucalyptus urophylla x E. grandis). Transcript levels of lignocellulose biosynthesis-related genes were studied.ResultsThe progeny plants had average WBD of 516 kg/m3 with normal distribution and did not show any correlations between WBD and wood volume or components of α-cellulose, hemicellulose and Klason lignin content. Transcriptomic analysis of two groups of five plants each with high (570–609 kg/m3) or low (378–409 kg/m3) WBD was carried out by RNA-Seq analysis with total RNAs extracted from developing xylem tissues at a breast height. Lignocellulose biosynthesis-related genes, such as cellulose synthase, invertase, cinnamate-4-hydroxylase and cinnamoyl-CoA reductase showed higher transcript levels in the high WBD group. Among plant cell wall modifying genes, increased transcript levels of several expansin and xyloglucan endo-transglycosylase/hydrolase genes were also found in high WBD plants. Interestingly, strong transcript levels of several cytoskeleton genes encoding tubulin, actin and myosin were observed in high WBD plants. Furthermore, we also found elevated transcript levels of genes encoding NAC, MYB, basic helix-loop-helix, homeodomain, WRKY and LIM transcription factors in the high WBD plants. All these results indicate that the high WBD in plants has been associated with the increased transcription of many genes related to lignocellulose formation.ConclusionsMost lignocellulose biosynthesis related genes exhibited a tendency to transcribe at relatively higher level in high WBD plants. These results suggest that lignocellulose biosynthesis-related genes may be associated with WBD.Electronic supplementary materialThe online version of this article (10.1186/s12870-018-1371-9) contains supplementary material, which is available to authorized users.
Defense gene expression systems of higher plants responsible for protection against pathogen attack are predominantly regulated by salicylic acid (SA)-and jasmonic acid (JA)-mediated pathways, and control the expression of many downstream defense response genes. To monitor the regulated gene expression of SA-mediated signaling pathways, we previously described an assay system based on the bioluminescence of seedlings transformed with a promoter-luciferase fusion gene. Here, to develop a system suitable for JA-mediated gene expression monitoring, we compared the expression patterns of Arabidopsis gene promoters obtained from the plant defensin 1.2 (PDF1.2) and vegetative storage protein 1 (VSP1) genes in response to treatment with chemicals. Although both promoters responded well to treatment with JA in 3-week-old plants, only the VSP1 promoter exhibited marked and prolonged luciferase expression in response to JA treatment in 6-dayold seedlings. The use of transgenic Arabidopsis seedlings harboring the VSP1-luciferase reporter gene construct enables multiwell plates to be used for conducting high-throughput assays for the screening of chemicals that are involved in JAmediated signaling pathways in Arabidopsis.Key words: Arabidopsis thaliana, firefly luciferase, high-throughput screening, jasmonic acid, PDF1.2, plant activator, VSP1.Plant defense responses are induced by various factors associated with pathogen infection and are predominantly mediated by signal transduction pathways regulated by salicylic acid (SA) and jasmonic acid (JA) (Pieterse et al. 2009). Numerous biological and natural agents capable of triggering defense responses have been commercialized as host defense inducers (Takahashi et al. 2006). Synthetic host defense inducers, such as probenazole (PBZ) and acibenzolar-s-methyl (ASM), have also been successfully used as agrochemicals for controlling plant diseases. Such defense inducers activate SA-mediated signaling pathways and are required for systemic acquired resistance (SAR), which is mainly involved in conferring resistance to biotrophic pathogens (Lawton et al. 1996; Yoshioka et al. 2001). To date, however, no synthetic host defense inducers involved in stimulating JA-mediated signaling pathways, which control defense responses against necrotrophic pathogens, are commercially available (Thomma et al. 2001).Compared with conventional fungicides, only a limited number of registered pesticides are classified as defense inducers, a fact that is mainly due to a lack of efficient screening and evaluation methods for the development of synthetic host defense inducers. To overcome this limitation, our group has been developing screening and evaluation methods based on the in vivo monitoring of defense gene expression using bioluminescence reporter gene technology (Ono et al. 2004;Tanaka et al. 2006). Recently, we established a highthroughput screening (HTS) and evaluation system for SAR inducers (Ono et al. 2011; Watakabe et al. 2011). The bioluminescence monitoring system allows us to...
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