Functional characterization of a novel Brassica LEAFY homolog from Indian mustard: Expression pattern and gain-of-function studies

- Expression domains of novel homolog (BjuLFY) is fine-mapped to stage 1-4 of primary floral buds in B. juncea suggesting its role in floral transition ; expression in root samples implied neo-functionalization.
- Similar LFY expression in early stages of bud development in 15 cultivars of 6 crop Brassica species implied functional conservation.
- Ectopic expression of BjuLFY in A. thaliana and B. juncea caused floral meristem defects and precocious flowering confirmed its role as floral regulator in B. juncea.
- GC-MS analysis of mature seed from Brassica transgenics showed an altered fatty-acid profile suggestive of seed maturation occurring at lower temperatures due to early flowering.

LEAFY plays a central role in regulation of flowering time and floral meristem identity in plants. Unfortunately, LFY function remains uncharacterized in agronomicaly important Brassicas. Herein, we illustrate fine-mapping of expression domains of LFY in 15 cultivars of 6 Brassica species and describe gain-of-function phenotypes in Arabidopsis and Brassica. We depict early flowering and altered fatty-acid composition in transgenic seed. The cDNA encoding BjuLFY (417aa) shared only 85% identity with reported homolog of B.juncea implying distinctness. Quantitative RT-PCR based coarse expression mapping of BjuLFY in tissue samples representing 3 time points at specific days after sowing (DAS), pre-flowering (30 DAS), flowering (75 DAS) and post-flowering (110 DAS), depicted an intense pulse of BjuLFY expression restricted to primary floral buds (75 DAS) which subsided in secondary floral buds (110 DAS); expression in root samples was also recorded implying neo-functionalization. Fine-mapping of expression during flowering confirmed tightly regulated LFY expression during early stages of bud development in 15 cultivars of 6 Brassica species implying functional conservation. Ectopic expression of BjuLFY in A. thaliana and B. juncea caused floral meristem defects and precocious flowering. B. juncea transgenics (T1) over-expressing BjuLFY flowered 20 days earlier produced normal flowers. GC-MS analysis of mature seed from Brassica transgenics showed an altered fatty-acid profile suggestive of seed maturation occurring at lower temperatures vis-à-vis control. Our findings implicate BjuLFY as a regulator of flowering in B. juncea and suggest its application in developing climate resilient crops.