S01 - Session O7 - The unique LcFT1 gene sequence linked to early-flowering in the tropical litchi 'Khom'

Authors: JenYu Chang *, Yi-Wen Ho, Chia-Nan Tao, Jer-Way Chang

Litchi ( Litchi chinensis ) was a royal tribute in ancient China. Today, it is still regarded as the most luxurious fresh fruit in summer because of the short harvest season. Floral induction in litchi is promoted by the expression of the FLOWERING LOCUS T (FT) homolog, LcFT1 , in winter when the leaves sense cool temperature. Two alleles of the LcFT1 promoter affect the sensitivity and expression level of the gene, resulting in early-flowering or late-flowering traits in Chinese origin litchi. Some litchi varieties are able to flower and produce in the tropical region of central Thailand, so called "tropical litchi", but their flowering mechanism is less understood. In this study we cloned and investigated the expression of the LcFT homolog from the early-season variety 'Sanyuehong', the mid-season variety 'Hak Ip', the late-season variety 'Rose Red' and the tropical litchi 'Khom'. Surprisingly, our results revealed a duplication of the partial promoter in the first intron of the LcFT1 of tropical litchi 'Khom', resulting in a 676 bp insertion. The 'Khom'-type LcFT1 produces identical transcripts as other varieties. Although this allele seems to be derived from the late-flowering-type, its expression is earlier than the late-flowering-type. On the other hand, sequence and expression of LcFT2 was conserved in the varieties we examined. Today, 'Khom' is used in litchi breeding in Taiwan to generate new varieties that can flower and bear fruit under increasing global warming. Our first findings on the 'Khom'-type LcFT1 identified a selective target for introgression of the flowering trait in litchi breeding.