Characterization of a novel dominant mutation BrCRSL conferring curled rod-shaped leaves in Chinese cabbage

Abstract

Leaf morphogenesis requires precise genetic control and hormone regulation to develop into ideal plant architectures. Leaf flattening is an adaptive trait to obtain efficient photosynthesis, for which the leaf adaxial–abaxial polar establishment is of great importance. Herein, a novel leaf morphological mutant, curled rod-shaped leaf (crsl), was isolated and characterized from Chinese cabbage (Brassica rapa L. ssp. pekinensis) EMS-induced population. The leaves in crsl were slender and rod-shaped, with the abaxial side folded upwards and the distal side curled downwards, the mesophyll cells were loosely arranged, and the epidermal morphology was opposite on the adaxial and abaxial surface. Genetic analysis revealed that the curled rod-shaped leaf mutant phenotype was controlled by a dominate nuclear gene, named BrCRSL. MutMap and Kompetitive Allele Specifc PCR (KASP) genotyping demonstrated that BraA02g016100.3C was the most likely candidate for BrCRSL. Compared with the wild-type, a non-synonymous SNP mutation (C to T) occurred in the 8th exon of BraA02g016100.3C in crsl. BraA02g016100.3C is orthologous of Arabidopsis thaliana MAB1 (AT5G50850), which encodes a putative mitochondrial PDH E1β subunit protein and contributes to PIN-dependent auxin transport in organ development. The amino acid substitution from proline (P) to leucine (L) is conserved among the homologous proteins of BraA02g016100.3C. ​The crsl mutant exhibited abnormal auxin metabolism, primarily manifested by high level of L-tryptophan (TRP) accumulation that is the precursor of IAA biosynthesis. Furthermore, the expression of a wide range of leaf adaxial/abaxial polarity-related genes was affected in crsl. Our results contribute to a better understanding of the genetic control mechanism underlying leaf morphogenesis in Chinese cabbage and provide new insights into the auxin-related leaf axial growth.