Preferential Distribution of Boron to Developing Tissues Is Mediated by the Intrinsic Protein OsNIP3

Abstract

Boron is especially required for the growth of meristem and reproductive organs, but the molecular mechanisms underlying the preferential distribution of B to these developing tissues are poorly understood. Here, we show evidence that a member of nodulin 26-like intrinsic protein (NIP), OsNIP3;1, is involved in this preferential distribution in rice (Oryza sativa). OsNIP3;1 was highly expressed in the nodes and its expression was up-regulated by B deficiency, but down-regulated by high B. OsNIP3;1 was polarly localized at the xylem parenchyma cells of enlarged vascular bundles of nodes facing toward the xylem vessels. Furthermore, this protein was rapidly degraded within a few hours in response to high B. Knockout of this gene hardly affected the uptake and root-to-shoot translocation of B, but altered B distribution in different organs in the above-ground parts, decreased distribution of B to the new leaves, and increased distribution to the old leaves. These results indicate that OsNIP3;1 located in the nodes is involved in the preferential distribution of B to the developing tissues by unloading B from the xylem in rice and that it is regulated at both transcriptional and protein level in response to external B level.

Boron Toxicity and Deficiency in Agricultural Plants

“…NIP6;1 is involved in boron transfer from the xylem to phloem [93] and NIP7;1 in microsporogenesis [94]. Homologous channels were found in barley, maize, and rice [95][96][97][98].…”

Boron demanding tissues of Brassica napus express specific sets of functional Nodulin26‐like Intrinsic Proteins and BOR1 transporters

“…This cooperative system ensures root B uptake, B root‐to‐shoot translocation and B loading into specific cells, tissues or the apoplast of different model and crop plant species (Takano et al ., ; Miwa et al ., ; Reid, ; Sutton et al ., ; Tanaka et al ., ; Kajikawa et al ., ; Miwa et al ., ; Chatterjee et al ., , ; Durbak et al ., ; Hanaoka et al ., ; Pallotta et al ., ; Hua et al ., ; Routray et al ., ; Shao et al ., ). Additionally, BORs and NIPs have been demonstrated to be decisive factors determining plant B toxicity tolerance (Miwa and Fujiwara, ).…”

Boron: More Than an Essential Element for Land Plants?

“…The preferential distribution of B in developing tissues of rice ( Oryza sativa ) is seemingly regulated in consonance with the expression of NIP , OsNIP3;1 ( Shao et al, 2018 ). Accordingly, knockout plants for this gene exhibited reductions in B content in newly developed leaves coupled with improved B translocation to old leaves, suggesting that OsNIP3;1 plays a key role in the distribution of B in developing tissues ( Shao et al, 2018 ).…”