Overexpression of Arabidopsis FLOWERING LOCUS T (FT) gene improves floral development in cassava (Manihot esculenta, Crantz)

Abstract

Cassava is a tropical storage-root crop that serves as a worldwide source of staple food for over 800 million people. Flowering is one of the most important breeding challenges in cassava because in most lines flowering is late and non-synchronized, and flower production is sparse. The FLOWERING LOCUS T (FT) gene is pivotal for floral induction in all examined angiosperms. The objective of the current work was to determine the potential roles of the FT signaling system in cassava. The Arabidopsis thaliana FT gene (atFT) was transformed into the cassava cultivar 60444 through Agrobacterium-mediated transformation and was found to be overexpressed constitutively. FT overexpression hastened flower initiation and associated fork-type branching, indicating that cassava has the necessary signaling factors to interact with and respond to the atFT gene product. In addition, overexpression stimulated lateral branching, increased the prolificacy of flower production and extended the longevity of flower development. While FT homologs in some plant species stimulate development of vegetative storage organs, atFT inhibited storage-root development and decreased root harvest index in cassava. These findings collectively contribute to our understanding of flower development in cassava and have the potential for applications in breeding.

Transgenic overexpression of endogenous FLOWERING LOCUS T-like gene MeFT1 produces early flowering in cassava

“…MeFT1 upregulation in the transgenic plants described here was also associated with increased transcript abundance of downstream floral meristem identity genes MeAP1, MeSOC1 and MeLFY (Fig 6). Correlating flowering in cassava with increased expression of native MeFT1 and floral meristem identity genes supports the hypothesis that the apical shoot of cassava has floral meristem identity genes that associate with FT genes to trigger flowering [20]. These mRNA profiles match findings in kiwifruit and jatropha expressing AcFT1, AcFT2 and JcFT transgenes that resulted in upregulation of floral identify genes LFY, SOC1 and AP1 [18,19].…”

“…Here we report production of inflorescences from plants lines transgenic for expression of MeFT1. These findings correlate with heterologous overexpression of AtFT in cassava [20,25] and represents first evidence for flower induction by manipulation of a native FT-like gene in cassava. A consequence of such rapid transition to the flower phase is commitment of meristems to produce inflorescences and termination of vegetative growth.…”

“…Recent studies with transgenic cassava plants of cv. 60444 expressing AtFT also recorded a negative correlation between robust flowering and cassava storage root production [20]. Combined, this evidence indicates that overexpression of FT is a strategy unlikely to enhance storage root production in cassava.…”

“…A BLAST search of the cassava genome database in Phytozome 11 (version 4.1) with Arabidopsis FT (AT1G65480.1) nucleotide sequence identified 10 FT family genes encoding PEBP [21]. We selected MeFT1 for gain of function studies based on its similarity with AtFT, the latter of which triggered early flowering when overexpressed in cassava [20]. The genomic sequence of MeFT1 was seen to consist of 1,987 nucleotides, within which there are four exons and three introns ( Fig 1A) that code for 175 amino acids.…”

“…Upon delivery to the shoot apical meristematic (SAM) region, FT and the bZIP transcription factor FLOWERING LOCUS D (FD) form a protein complex which further interacts with SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1), APETALA 1 (AP1) and LEAFY (LFY) proteins to induce flowering [15][16][17]. Transition to reproductive development by FT upregulation have been associated with a measurable increase in mRNA levels of both FT and downstream floral meristem identity genes in the SAM [18][19][20].…”