Enhanced Boron Tolerance in Plants Mediated by Bidirectional Transport Through Plasma Membrane Intrinsic Proteins

Abstract

High boron (B) concentration is toxic to plants that limit plant productivity. Recent studies have shown the involvement of the members of major intrinsic protein (MIP) family in controlling B transport. Here, we have provided experimental evidences showing the bidirectional transport activity of rice OsPIP1;3 and OsPIP2;6. Boron transport ability of OsPIP1;3 and OsPIP2;6 were displayed in yeast HD9 mutant strain (∆fps1∆acr3∆ycf1) as a result of increased B sensitivity, influx and accumulation by OsPIP1;3, and rapid efflux activity by OsPIP2;6. RT-PCR analysis showed strong upregulation of OsPIP1;3 and OsPIP2;6 transcripts in roots by B toxicity. Transgenic Arabidopsis lines overexpressing OsPIP1;3 and OsPIP2;6 exhibited enhanced tolerance to B toxicity. Furthermore, B concentration was significantly increased after 2 and 3 hours of tracer boron (10B) treatment. Interestingly, a rapid efflux of 10B from the roots of the transgenic plants was observed within 1 h of 10B treatment. Boron tolerance in OsPIP1;3 and OsPIP2;6 lines was inhibited by aquaporin inhibitors, silver nitrate and sodium azide. Our data proved that OsPIP1;3 and OsPIP2;6 are indeed involved in both influx and efflux of boron transport. Manipulation of these PIPs could be highly useful in improving B tolerance in crops grown in high B containing soils.

Boron toxicity in higher plants: an update

“…Plasma membrane Intrinsic Proteins (PIPs) have also been shown to be involved in mediating B permeability, thereby modulating B movement and increasing B tolerance. More recently, two representative rice PIP genes, OsPIP1;3 and OsPIP2;6, were reported to function as influx and efflux bidirectional transporters and conferred an enhanced B tolerance when overexpressed in Arabidopsis plants (Mosa et al 2016).…”

Genome-Wide Identification and Characterization of the Aquaporin Gene Family and Transcriptional Responses to Boron Deficiency in Brassica napus

“…Yeast complementation assays have confirmed that HvPIP1;3 and HvPIP1;4 can facilitate B transport across the membranes into yeast cells (Fitzpatrick and Reid, 2009 ). However, the overexpression of AtTIP5;1 and rice OsPIP2;4, OsPIP2;7, OsPIP1;3 , and OsPIP2;6 in Arabidopsis notably increased its tolerance to high levels of B, and the latter two are involved the influx and efflux transport of B (Pang et al, 2010 ; Kumar et al, 2014 ; Mosa et al, 2015 ). In addition, AQP proteins can also facilitate transport of many other small molecule nutrients, such as Lis1 (OsNIP2;1) for silicon transport (Ma et al, 2006 ), AtTIP2;1 and AtTIP2;3 for NH 3 transport (Loqué et al, 2005 ), AtNIP3;1 for arsenic uptake (Xu et al, 2015 ), and AtNIP1;2 facilitating Al-malate transport (Wang Y. et al, 2017 ), respectively.…”

Structure of Bor1 supports an elevator transport mechanism for SLC4 anion exchangers

“…The regulation of boron by transporters is therefore important for plant viability and has implications for worldwide agriculture. Indeed, there are ongoing efforts to engineer plants that are tolerant of either high or low boron levels in soil (6)(7)(8). The transport and regulation of boron levels is regulated partly by Bor1, a boron exporter that loads xylem, such that boron is transported from roots to shoots and leaves (3).…”