Abstract
BackgroundBoron (B)-toxicity is an important disorder in agricultural regions across the world. Seedlings of ‘Sour pummelo’ (Citrus grandis) and ‘Xuegan’ (Citrus sinensis) were fertigated every other day until drip with 10 μM (control) or 400 μM (B-toxic) H3BO3 in a complete nutrient solution for 15 weeks. The aims of this study were to elucidate the adaptive mechanisms of citrus plants to B-toxicity and to identify B-tolerant genes.ResultsB-toxicity-induced changes in seedlings growth, leaf CO2 assimilation, pigments, total soluble protein, malondialdehyde (MDA) and phosphorus were less pronounced in C. sinensis than in C. grandis. B concentration was higher in B-toxic C. sinensis leaves than in B-toxic C. grandis ones. Here we successfully used cDNA-AFLP to isolate 67 up-regulated and 65 down-regulated transcript-derived fragments (TDFs) from B-toxic C. grandis leaves, whilst only 31 up-regulated and 37 down-regulated TDFs from B-toxic C. sinensis ones, demonstrating that gene expression is less affected in B-toxic C. sinensis leaves than in B-toxic C. grandis ones. These differentially expressed TDFs were related to signal transduction, carbohydrate and energy metabolism, nucleic acid metabolism, protein and amino acid metabolism, lipid metabolism, cell wall and cytoskeleton modification, stress responses and cell transport. The higher B-tolerance of C. sinensis might be related to the findings that B-toxic C. sinensis leaves had higher expression levels of genes involved in photosynthesis, which might contribute to the higher photosyntheis and light utilization and less excess light energy, and in reactive oxygen species (ROS) scavenging compared to B-toxic C. grandis leaves, thus preventing them from photo-oxidative damage. In addition, B-toxicity-induced alteration in the expression levels of genes encoding inorganic pyrophosphatase 1, AT4G01850 and methionine synthase differed between the two species, which might play a role in the B-tolerance of C. sinensis.ConclusionsC. sinensis leaves could tolerate higher level of B than C. grandis ones, thus improving the B-tolerance of C. sinensis plants. Our findings reveal some novel mechanisms on the tolerance of plants to B-toxicity at the gene expression level.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-014-0284-5) contains supplementary material, which is available to authorized users.
Highlights
Boron (B)-toxicity is an important disorder in agricultural regions across the world
We found that B-toxicity increased the expression levels of genes encoding cytochrome P450 (TDF #5_1) and cytochrome P450 like protein (TDF #76-1) in C. grandis leaves (Table 2), which agrees with the previous report that some of the 49 cytochrome P450 genes in Arabidopsis were upregulated by biotic (i.e., Alternaria brassicicola and Alternaria alternata) and abiotic [i.e., drought, high salinity, low temperature, hormones, paraquat, rose bengal, UV stress (UV-C), mechanical wounding and heavy metal stress (CuSO4)] stresses [29]
Our result showed that the transcript level of transducin/WD40 domain-containing protein (ATG18a, transcript-derived fragments (TDFs) #104_3) in C. sinensis leaves decreased in response to B-toxicity (Table 2), indicating that autophagy is impaired in C. sinensis leaves
Summary
Boron (B)-toxicity is an important disorder in agricultural regions across the world. The aims of this study were to elucidate the adaptive mechanisms of citrus plants to B-toxicity and to identify B-tolerant genes. Kasajima and Fujiwara first investigated high B-induced changes in gene expression in Arabidopsis thaliana roots and rosette leaves using microarray, and identified a number of high B-induced genes, including a heat shock protein and a number of the multi-drug and toxic compound extrusion (MATE) family transporters [5]. Aquea et al found that B-toxicity upregulated the expression of genes related to ABA signaling, ABA response and cell wall modification, and downregulated the expression of genes involved in water transporters in Arabidopsis roots, concluding that root growth inhibition was caused by B-toxicity-induced water-stress [7]. Most research has focused on roots and herbaceous plants (i.e., barley, A. thaliana), very little is known about the differential expression of genes in response to B-toxicity in leaves and woody plants
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