CRISPR / Cas9 ‐mediated mutation of BnaA5.JAR1 alleviates boron deficiency stress by enhancing calcium‐pectin cross‐linki

SUMMARY

Boron (B) is an essential micronutrient critical for plant growth and reproductive development, primarily through its role in the cell wall. Calcium (Ca ²⁺ ) similarly stabilizes cell wall architecture by forming cross‐links with de‐esterified pectin. In Arabidopsis thaliana , B deficiency rapidly induces JASMO0NATE RESISTANT 1 ( JAR1 ) and jasmonic acid (JA) accumulation, which negatively regulates growth. However, whether and how JAR1 ‐mediated JA signaling modulates cell wall B and Ca ²⁺ partitioning to confer B‐deficiency tolerance remains unclear. Here, we characterized the function of BnaA5.JAR1 in rapeseed ( Brassica napus L.) under B deficiency. Pharmacological inhibition of JA biosynthesis with ibuprofen partially alleviated B‐deficiency‐induced shoot growth inhibition. BnaA5.JAR1 transcript levels were rapidly and strongly induced by B deprivation. CRISPR/Cas9‐mediated knockout of BnaA5.JAR1 enhanced tolerance to B deficiency, whereas overexpression increased sensitivity, despite unchanged leaf B concentrations. Notably, mutant lines maintained robust tolerance throughout the reproductive stage, effectively rescuing the ‘flowering without seed setting’ phenotype characteristic of B deficiency. Under B limitation, these knockout lines retained higher B and Ca ²⁺ concentrations in alkali‐soluble pectin, exhibited a lower degree of pectin methylesterification, and maintained thinner, more structurally normal cell walls compared with overexpression lines. Exogenous Ca ²⁺ mitigated B deficiency symptoms without increasing leaf B concentration. Collectively, these findings establish BnaA5.JAR1 as a negative regulator of B‐deficiency tolerance and demonstrate that suppressing its activity enhances Ca ²⁺ ‐mediated cell wall stabilization across vegetative and reproductive stages, offering a targeted molecular strategy for breeding B‐efficient rapeseed cultivars.