Stem mustard (Brassica juncea var. tumida Tsen et Lee) is an important economic vegetable in China. Premature bolting induced by temperature fluctuations has become a major cultivation constraint. Photoreceptors (PHRs) serve as critical photosensor proteins that interpret light signals and regulate physiological responses in plants. In this study, five core PHR families, namely F-box-containing flavin binding proteins (ZTL/FKF1/LKP2), phytochrome (PHY), cryptochrome (CRY), phototropin (PHOT) and UV RESISTANCE LOCUS 8 (UVR8) were identified in Brassica species. RNA-seq analysis revealed their expression patterns during organogenesis in B. juncea. Seven candidate PHRs were validated by qRT-PCR in B. juncea early-bolting (‘YA-1’) and late-bolting (‘ZT-1’) cultivars. Agrobacterium-mediated BjuFKF1₁ overexpression (OE) lines resulted in significantly earlier flowering under field conditions. Histochemical GUS staining indicated that BjuFKF1₁ was expressed in seedlings, leaves, flower buds and siliques. Transcript analysis revealed that the expression level of BjuFKF1₁ was up-regulated in all tissues at both the vegetative and reproductive stages, whereas the expression of BjuFKF1₁ interacting protein-encoding genes were down-regulated in flowers. Under blue light, genes encoding interacting proteins (BjuCOL5, BjuSKP1, BjuCOL3, BjuAP2, BjuAP2-1 and BjuLKP2) were up-regulated in flower buds, whereas BjuCOL and BjuPP2C52 were down-regulated in flowers. Developmental stage analysis revealed the up-regulation of five (BjuAP2, BjuCOL3, BjuCOL5, BjuAP2-1 and BjuLKP2) and four (BjuCOL, BjuCOL5, BjuAP2 and BjuLKP2) interaction protein-encoding genes during the reproductive stage under white and blue light, respectively. These findings elucidate the role of BjuFKF1₁ in flowering regulation and provide molecular targets for B. juncea bolting-resistant variety breeding.
Gao et al. (Thu,) studied this question.