Differential Expression Of Genes In Citrus Seedlings Under Magnesium Deficiency Based On CDNA-AFLP

‘Ponkan’(Citrus reticulate) seedlings were used as material in this study. Genesinvolved in magnesium (Mg)-deficiency were screened and analysed throughcDNA-AFLP. The mechanism of ‘Ponkan’ plants in response to Mg-deficiency wasstudied by analyzing different gene expression levels in different tissues. Theobjective of this study was to provide a scientific basis for the high yield and qualitycultivation of citrus. The main findings were as follows:1. Mg-deficient symptoms firstly appeared in the older leaves and were patchychlorotic on both sides of midrib and between the main veins, with leaf apex and leafbase remaining green. Leaves abscised from the shoot easily. Mg-deficiencydecreased the dry weight of roots, shoots and total plant and exerted a lager influenceon root dry weigt compared with shoot dry weight. Under Mg-deficiency,‘Ponkan’seedling biomass declined, the aging of old leaves were accelerated and normalgrowth was inhibited.2. A total of256primer combinations were used to the cDNA-AFLP-basedtranscript profiling of ‘Ponkan’ roots and leaves in response to Mg-deficiency. Eachprimer pair amplified15-40transcript-derived fragments (TDFs). Seventy twodifferential expressed TDFs were obtained from roots including12putative andunknown TDFs. The remaining60TDFs showed great homologous with Arabidopsisthaliana and Medicago truncatula species. GO annotation function analysis showedthe60TDFs in response to Mg-deficiency were involved in carbohydrate metabolism,tissue synthesis, stress response, growth and development, redox metabolism, proteinmetabolism, signal transduction, transcription and translation, transport. In leaves,70differential expressed TDFs were obtained including12putative and unknown TDFs.The remaining58TDFs were involved in photosynthesis, carbohydrate metabolism,synthesis of cells and tissues, adversity response, redox reactions, protein metabolism,signal transduction, transcription and translation, transport and so on.3. In roots, Mg-deficiency up-regulated the expression levels of genes involvedin carbohydrate metabolisom including homogentisic acid phytol transferase genes,short-chain alcohol dehydrogenase, DTDP-glucose4,6-dehydratase gene, glucosephosphate mutase genes and of genes involved in mineral nutrient uptake cysteine-rich repeat sequences, purple acid phosphatase gene.4. In leaves, Mg-deficiency up-regulated the expression levels of genes encodingpolyubiquitin and calcium-dependent lipid-binding domain. Mg-deficiency-inducedchanges in the expression levels of genes encoding F-box domain protein, leucine-richrepeat sequence receptor-like protein kinase, cytochrome P450and early response todehydration were similar between roots and leaves. It was concluded that the adaptiveresponse of citrus to Mg-deficiency is co-regulated via multiple physiologicalmetabolic pathways.