The boron transporter <i>BnaC4.BOR1;1c</i> is critical for inflorescence development and fertility under boron limitation in <scp><i>Brassica napus</i></scp>

<jats:title>Abstract</jats:title><jats:p>Boron (B) is an essential micronutrient for plants, but the molecular mechanisms underlying the uptake and distribution of B in allotetraploid rapeseed (<jats:styled-content style="fixed-case"><jats:italic>Brassica napus</jats:italic></jats:styled-content>) are unclear. Here, we identified a B transporter of rapeseed, <jats:italic>BnaC4.BOR1;1c</jats:italic>, which is expressed in shoot nodes and involved in distributing B to the reproductive organs. Transgenic <jats:italic>Arabidopsis</jats:italic> plants containing a <jats:italic>BnaC4.BOR1;1c</jats:italic> promoter‐driven GUS reporter gene showed strong GUS activity in roots, nodal regions of the shoots and immature floral buds. Overexpressing <jats:italic>BnaC4.BOR1;1c</jats:italic> in <jats:italic>Arabidopsis</jats:italic> wild type or in <jats:italic>bor1‐1</jats:italic> mutants promoted wild‐type growth and rescued the <jats:italic>bor1‐1</jats:italic> mutant phenotype. Conversely, knockdown of <jats:italic>BnaC4.BOR1;1c</jats:italic> in a B‐efficient rapeseed line reduced B accumulation in flower organs, eventually resulting in severe sterility and seed yield loss. <jats:italic>BnaC4.BOR1;1c</jats:italic> RNAi plants exhibited large amounts of disintegrated stigma papilla cells with thickened cell walls accompanied by abnormal proliferation of lignification under low‐B conditions, indicating that the sterility may be a result of altered cell wall properties in flower organs. Taken together, our results demonstrate that <jats:italic>BnaC4.BOR1;1c</jats:italic> is a <jats:italic>AtBOR1</jats:italic>‐homologous B transporter gene expressing in both roots and shoot nodes that is essential for the developing inflorescence tissues, which highlights its diverse functions in allotetraploid rapeseed compared with diploid model plant <jats:italic>Arabidopsis</jats:italic>.</jats:p>