| Nutrition deficiencies, especially iron (Fe) and boron (B) deficiencies are wildly existed in citrus mountain orchards in south of China. Omics is a rapidly developing biotechnology with characteristics of high throughput, accurateness, quantitative analysis and high depth resolution,which is widely used in the researches of biology. Omics can comprehensively reveal the molecular mechanism from genome, transcription and translation levels. In this research, the molecular responses to Fe and B deficiencies were investigated by transcriptome, small RNA and ionomic analysis. The major results were listed as follows:1 The omics research of Fe deficiency in citrusTranscript difference was compared in the leaves of fragrant citrus (Citrus jonus) between Fe deficient (ID) and sufficient (IS) treatments through hydroponics.(1)913 genes were differently expressed between ID and IS leaves. Of them, 598 genes were upregulated and 315 genes were downregulated by Fe deficiency. These differently expressed genes were involved in 91 pathways, in which chlorophyll metabolism, photosynthesis (contain antenna proteins) and nitrogen metabolism were closely related to citrus iron deficiency chlorosis.The expression levels of glutamyl-tRNA reductase, chlorophyll (ide) b reductase and geranylgeranyl diphosphate reductase genes were significantly decreased in ID leaves than those in IS leaves, and the expression levels of chlorophyllide a oxygenase was significantly increased in chlorosis leaves than those in the normal leaves. The expression levels of 16 photosynthesis-related genes were severely downregulated by Fe deficiency. In addition, the transcription levels of nitrate transporter, nitrate reductase and ferredoxin-nitrite reductase genes was significantly increased in ID leaves than those in IS leaves. Taken together, these results indicated that the block of Ch1 biosynthesis, the reduction of photosynthesis and the repression of nitrogen absorption resulted in the chlorosis symptoms observed in fragrant citrus leaves.(2) 147 known and 427 novel miRNAs were identified in the leaves of this Fe-deficient experiment. Of them, 50 (10 known and 40 novel) up- and 31 (16 known and 15 novel)down-regulated miRNAs were isolated from Fe-deficient leaves, indicating that miRNA might contribute to the tolerance of citrus to Fe-deficiency. In them, 6 of this miRNAs may play important roles in enhancing the tolerance against Fe-deficiency. In detail, In detail, miR172 which responses to stress was downregulated and might play a role in enhancing the leaves tolerance of Fe deficiency; miR319 and miR477 which were related to growth and development were upregulated and might play a role in inhibiting the plant growth; miR397, miR398 and miR408 which were related to antioxidation were downregulated and might play a role in enhancing Cu/Zn superoxide dismutase activity. On the other hand, miR397and miR408 which are related to lignin biosynthesis were downregulated and might play a role in promoting lignin accumulation.2 The omics research of B deficiency in citrusTo investigate the molecular mechanism of scion affected B absorption in rootstock, Newhall(B-efficient) navel orange (Citrus sinensis)/trifoliate orange and Fengjie (B-inefficient) navel orange/trifoliate orange were used as materials to investigate the transcript difference in the roots between B deficient (BD) and sufficient (BS) treatments through sand-culture.(1) The B content, B accumulation and B distribution existed differently between different tissues of two navel orange. Under BS condition, the B contents in the whole plant, the roots or leaves were significantly higher in the Newhall than those in the Fengjie; Under BD condition,the B content in the whole plant showed no significant different between the two cultivars while the B contents in Newhall mature or young leaves were significantly lower than those in Fengjie mature or young leaves. In addition, the content of usable B (free and semi-bound B) in the leaves of Newhall was significantly lower than those in Fengjie, while versa in the root.(2) B deficiency significantly affected the root IAA, ABA and lignin contents. Under BS condition, there had no significant difference in the contents of IAA, ABA and lignin between the roots of the two cultivars. However under BD condition, the decreasing degree of IAA was significantly higher, the increasing degree of ABA was significantly lower in Newhall than in Fengjie. In addition, the increasing degree of lignin was significantly higher in Newhall than in Fengjie.(3) Genes of aquaporins (NIP5;1, PIP2;2, TIP1;3 and TIP2;2), ethylene and ABA synthesis-related or signal transduction-related (ACO11 ERF, NCED1, SnRK) were significantly induced in the root of Fengjie than those in the root of Newhall. As compared to Newhall, the expression levels of IAA hydrolase-related genes (ILR1 and ILR4) were significantly reduced in the root of Fengjie. Moreover, the increasing degree of ligninsynthesis genes (PAL, COMT and POD) were significantly higher in Newhall than those in Fengjie.3 Investigating the role of miR397 in the response to B toxicityBy using trifoliate orange as material, the effect of B toxicity on the gene expression of miR397 and LAC7 (miR397 putative target gene), the activity of laccase and the lignin content was studied through hydroponics. Results showed that B toxicity significantly increased the root or leaf B content, the LAC7 expression level, the lasccase activity and lignin content but significantly reduced the miR397 expression level. Because LAC7 is the putative target of miR397 and LAC7 plays a role in lignin biosynthesis, these results therefore suggested that decreased miR397 transcription plays a possible role in enhancing tolerance to B toxicity stress via negatively regulating LAC7 transcription and increasing the lignin concentration. |
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