Transcription factor BnaA1.WRKY53 is involved in regulation of auxin-induced leaf curling under boron deficiency in Brassica napus

Brassica napus (oilseed rape) is sensitive to boron (B) deficiency and exhibits young leaf curling in response to low-B stress at the seedling stage, which leads to reduced photosynthesis and plant growth. So far, no gene has been identified to be involved in B deficiency induced leaf curling. Our previous results showed the transcription factor BnaA1.WRKY53 might be involved in B-deficiency tolerance. However, altered BnaA1.WRKY53 expression does not influence B concentration in shoot, root and leaf cell walls, which suggests BnaA1.WRKY53 might be involved in other biological processes. Indeed, phenotypic and anatomical analyses revealed that BnaA1.WRKY53 negatively regulated the leaf curling induced by leaf epinasty by suppressing the overexpansion of palisade cells under B deficiency. Further transcriptome enrichment analysis of differentially expressed genes (DEGs) between wild-type and BnaA1.WRKY53 overexpression line showed auxin response pathway was enriched. In addition, Arabidopsis DR5::GFP auxin reporter line showed B deficiency caused predominant auxin signal accumulation in the adaxial side and concomitant adaxial cell expansion, which indicated that B deficiency may induce leaf curling by altering auxin distribution. Phytohormone quantification and gene expression analysis demonstrated that BnaA1.WRKY53 prevent auxin overaccumulation in leaves by suppressing auxin biosynthetic genes under B deficiency. Furthermore, exogenous 1-naphthlcetic acid (NAA) treatment experiments revealed that high auxin could induce leaf curling and BnaA1.WRKY53 expression. Overall, these findings demonstrate that auxin and the transcription factor BnaA1.WRKY53 synergistically regulate leaf curling to maintain an optimal leaf area under B deficiency, and provide novel insights into the resistance mechanisms against B-deficiency-induced leaf curling in oilseed rape.