Abstract
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.
Highlights
In plants, phytic acid is a major storage form of seed phosphate that chelates important micronutrients (Ca, Zn, Mg, Fe, Mn, etc.) and reduces their bio-availability (Sandberg and Andersson, 1988; Raboy, 2001, 2009)
TaABCC13 was mapped to the long arm of the 4B, 4D, and 5A chromosomes with a similarity score of 99% and 97% (4B allele with respect to 4D and 5A)
The expression of all TaABCC13 homoeologous transcripts was higher at 14 d after anthesis (DAA) than at 21 DAA
Summary
Phytic acid (myo-inositol 1,2,3,4,5,6-hexakisphosphate; PA; IP6) is a major storage form of seed phosphate that chelates important micronutrients (Ca, Zn, Mg, Fe, Mn, etc.) and reduces their bio-availability (Sandberg and Andersson, 1988; Raboy, 2001, 2009). Mutants similar to maize lpa with defects in MRP (ABCC type) transporter activity have been recovered from Arabidopsis (ABCC5; Nagy et al, 2009), barley (ABCC1; Dorsch et al, 2003), soybean (ABCC1; Panzeri et al, 2011), and rice (MRP5; Xu et al, 2009). These observations have encouraged reverse genetic approaches in crop plants to further validate the role of ABCC transporters in lowering the PA content. The lpa mutations have been most predominantly examined, with breeding and genetic engineering efforts in multiple plants (Supplementary Table S1 at JXB online)
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