Silencing of ABCC13 transporter in wheat reveals its involvement in grain development, phytic acid accumulation and lateral root formation

Low phytic acid is a trait desired in cereal crops and can be achieved by manipulating the genes involved either in its biosynthesis or its transport in the vacuoles. Previously, we have demonstrated that the wheat TaABCC13 protein is a functional transporter, primarily involved in heavy metal tolerance, and a probable candidate gene to achieve low phytate wheat. In the current study, RNA silencing was used to knockdown the expression of TaABCC13 in order to evaluate its functional importance in wheat. Transgenic plants with significantly reduced TaABCC13 transcripts in either seeds or roots were selected for further studies. Homozygous RNAi lines K1B4 and K4G7 exhibited 34-22% reduction of the phytic acid content in the mature grains (T4 seeds). These transgenic lines were defective for spike development, as characterized by reduced grain filling and numbers of spikelets. The seeds of transgenic wheat had delayed germination, but the viability of the seedlings was unaffected. Interestingly, early emergence of lateral roots was observed in TaABCC13-silenced lines as compared to non-transgenic lines. In addition, these lines also had defects in metal uptake and development of lateral roots in the presence of cadmium stress. Our results suggest roles of TaABCC13 in lateral root initiation and enhanced sensitivity towards heavy metals. Taken together, these data demonstrate that wheat ABCC13 is functionally important for grain development and plays an important role during detoxification of heavy metals.

Cadmium-inducible expression of the ABC-type transporter AtABCC3 increases phytochelatin-mediated cadmium tolerance in Arabidopsis

The heavy metal cadmium (Cd) is a widespread environmental contaminant with harmful effects on living cells. In plants, phytochelatin (PC)-dependent Cd detoxification requires that PC-Cd complexes are transported into vacuoles. Here, it is shown that Arabidopsis thaliana seedlings defective in the ABCC transporter AtABCC3 (abcc3) have an increased sensitivity to different Cd concentrations, and that seedlings overexpressing AtABCC3 (AtABCC3ox) have an increased Cd tolerance. The cellular distribution of Cd was analysed in protoplasts from abcc3 mutants and AtABCC3 overexpressors grown in the presence of Cd, by means of the Cd-specific fluorochromes 5-nitrobenzothiazole coumarin (BTC-5N) and Leadmium™ Green AM dye. This analysis revealed that Cd is mostly localized in the cytosol of abcc3 mutant protoplasts whereas there is an increase in vacuolar Cd in protoplasts from AtABCC3ox plants. Overexpression of AtABCC3 in cad1-3 mutant seedlings defective in PC production and in plants treated with l-buthionine sulphoximine (BSO), an inhibitor of PC biosynthesis, had no effect on Cd tolerance, suggesting that AtABCC3 acts via PCs. In addition, overexpression of AtABCC3 in atabcc1 atabcc2 mutant seedlings defective in the Cd transporters AtABCC1 and AtABCC2 complements the Cd sensitivity of double mutants, but not in the presence of BSO. Accordingly, the level of AtABCC3 transcript in wild type seedlings was lower than that of AtABCC1 and AtABCC2 in the absence of Cd but higher after Cd exposure, and even higher in atabcc1 atabcc2 mutants. The results point to AtABCC3 as a transporter of PC-Cd complexes, and suggest that its activity is regulated by Cd and is co-ordinated with the activity of AtABCC1/AtABCC2.