CDNA-AFLP Analysis On Gene Expression In Response To Boron-aluminum Interactions In Roots Of Citrus Grandis

The physiological and biochemical mechanisms on boron (B)-induced alleviation of aluminum (B)-toxicity in plants have been examined in some details, but our understanding of the molecular mechanisms underlying these processes is very limited. Seedlings of ’Sour pummelo’ (Citrus grandis) were supplied with nutrient solution containing two B (i.e.,2.5 and 20 μM H3BO3) × two Al [i.e.,0 (-Al) and 1.2 mM AlCl3-6 H2O (+Al)] levels for 18 weeks. The objectives of this study were to understand the gene expression patterns in Citrus grandis roots responsive to B and Al interactions.Our results showed that the effects of Al-toxicity on root dry weight (DW), shoot DW and root DW/shoot DW ratio were less pronounced under 20 μM B than under 2.5 μM B. Al-toxicity increased or did not affect B concentration in roots. In+Al seedlings, root Al concentration did not differ between two B treatments. Al-induced secretion of malate and citrate from +Al or -Al excised roots was not affected by B supply.In this study, we first used the cDNA-AFLP to isolate 100 differentially expressed genes. These differentially expressed genes were associated with metabolism (21), stress response (10), autophagy and senescence (15), signal transduction and hormone (12), gene regulation (15), cell transport (12), cell wall modification (4) and others (11). Functional analysis showed that genes related to detoxification of reactive oxygen species (ROS) and aldehydes (i.e., glutathione S-transferase zeta class-like isoform X1, thioredoxin M-type 4, and 2-alkenal reductase (NADP+-dependent )-like), metabolism (i.e., carboxylesterases and lecithin-cholesterol acyltransferase-like 4-like, nicotianamine aminotransferase A-like isoform X3, thiosulfate sulfurtransferase 18-like isoform X1, and ferredoxin-NADP reductase (FNR), root isozyme 2), cell transport (i.e., non-specific lipid-transfer protein-like protein At2g13820-like and major facilitator superfamily protein), Ca signal and hormone (i.e., calcium-binding protein CML19-like and IAA-amino acid hydrolase ILR1-like 4-like), gene regulation (i.e., Gag-pol polyprotein) and cell wall modification (i.e., glycosyl hydrolase family 10 protein) might play a role in B-induced alleviation of Al-toxicity. Our results are useful not only for our understanding on molecular processes associated with B-induced alleviation of Al-toxicity, but also for obtaining key molecular genes to enhance Al-tolerance of plants in the future.