NIP6;1 Is a Boric Acid Channel for Preferential Transport of Boron to Growing Shoot Tissues inArabidopsis

Abstract

Boron (B) in soil is taken up by roots through NIP5;1, a boric acid channel, and is loaded into the xylem by BOR1, a borate exporter. Here, the function of Arabidopsis thaliana NIP6;1, the most similar gene to NIP5;1, was studied. NIP6;1 facilitates the rapid permeation of boric acid across the membrane but is completely impermeable to water. NIP6;1 transcript accumulation is elevated in response to B deprivation in shoots but not in roots. NIP6;1 promoter–β-glucuronidase is predominantly expressed in nodal regions of shoots, especially the phloem region of vascular tissues. Three independently identified T-DNA insertion lines for the NIP6;1 gene exhibited reduced expansion of young rosette leaves only under low-B conditions. B concentrations are reduced in young rosette leaves but not in the old leaves of these mutants. Taken together, these data strongly suggest that NIP6;1 is a boric acid channel required for proper distribution of boric acid, particularly among young developing shoot tissues. We propose that NIP6;1 is involved in xylem–phloem transfer of boric acid at the nodal regions and that the water-tight property of NIP6;1 is important for this function. It is proposed that during evolution, NIP5;1 and NIP6;1 were diversified in terms of both the specificity of their expression in plant tissues and their water permeation properties, while maintaining their ability to be induced under low B and their boric acid transport activities.

A Transporter at the Node Responsible for Intervascular Transfer of Silicon in Rice

“…This is also supported by the fact that when Lsi6 was knocked out, the translocation of silicon to the panicles was greatly reduced ( Figure 4A). Recently, a boric acid channel from Arabidopsis thaliana (NIP6;1) was reported to be involved in the preferential transport of boron to growing shoot tissues (Tanaka et al, 2008). However, NIP6;1 is located at the phloem especially at the nodal region of the stem and petioles, suggesting that NIP6;1 is responsible for the xylem-phloem transfer of boric acid (Tanaka et al, 2008) but not for the intervascular transfer.…”

Boron toxicity tolerance in wheat and barley: Australian perspectives

“…Arsenite is the predominant form of arsenic (As) in paddy soils. It has previously been suggested that aquaporins may have a role in boron transport in higher plants (Dordas et al 2000, Fitzpatrick and and it was also shown in Arabidposis thaliana that a specific NIP subclass aquaporin gene (AtNIP5;1) is required for normal growth under B limiting conditions (Takano et al 2006, Tanaka et al 2008. NIP5;1 is strongly up-regulated in B-deprived roots and knockout mutants for this gene are defective in low Binducible boric acid uptake into roots (Takano et al 2006).…”

Roles of BOR2, a Boron Exporter, in Cross Linking of Rhamnogalacturonan II and Root Elongation under Boron Limitation in Arabidopsis

“…Takano et al (2006) identified nodulin26-like intrinsic protein5;1 (NIP5;1) in Arabidopsis as a boric acid channel required for efficient uptake into root cells under B-limited conditions. Arabidopsis NIP6;1, the gene most similar to NIP5;1, contributes to the preferential distribution of B in young shoot tissues (Tanaka et al, 2008).…”