Characterization of Cry2 genes (CRY2a and CRY2b) of B. napus and comparative analysis of BnCRY1 and BnCRY2a in regulating seedling photomorphogenesis

Key message Brassica napus (2n = 38, AACC) is an allotetraploid derived from cross-hybridization of B. rapa (2n = 20, AA) and B. oleracea (2n = 18, CC), followed by chromosome doubling. It is an important oilseed crop, and therefore, efforts are being made to enhance its agronomic traits. Early flowering is one of the essential agronomic traits which the breeders have long targeted in order to shorten the life cycle of Brassica. Early flowering along with delayed maturity, and high leaf area index lead to increase in seed yield. Due to the problem of global warming, high temperature during the terminal stage of a crop can result in significant yield loss as high temperature has a negative effect on bud formation to silique development stage. In this research article, we have reported that overexpression of BnCRY2a in Brassica juncea results in early flowering. This opens the door for making early flowering variety of Brassica napus a reality without any yield penalty. In-depth analysis of the pathway BnCRY2a follows to cause early flowering phenotype will significantly enhance our knowledge on the mechanism of flowering in oilseed crop plants. Cryptochrome 2 (CRY2) perceives blue/UV-A light and regulates photomorphogenesis in plants. However, besides Arabidopsis, CRY2 has been functionally characterized only in native species of japonica rice and tomato. In the present study, the BnCRY2a, generating a relatively longer cDNA and harboring an intron in its 5 ' UTR, has been characterized in detail. Western blot analysis revealed that BnCRY2a is light labile and degraded rapidly by 26S proteasome when seedlings are irradiated with blue light. For functional analysis, BnCRY2a was over-expressed in Brassicajuncea, a related species more amenable to transformation. The BnCRY2a over-expression (BnCRY2a(OE)) transgenics developed short hypocotyl and expanded cotyledons, accumulated more anthocyanin in light-grown seedlings, and displayed early flowering on maturity. Early flowering in BnCRY2a(OE) transgenics was coupled with the up-regulation of many flowering-related genes such as FT. The present study also highlights the differential light sensitivity of cry1 and cry2 in controlling hypocotyl elongation growth in Brassica. BnCRY2a(OE) seedlings developed much shorter hypocotyl under the low-intensity of blue light, while BnCRY1(OE) seedling hypocotyls were shorter under the high-intensity blue light, compared to untransformed seedlings.