Litchi Flowering is Regulated by Expression of Short Vegetative Phase Genes

Abstract

<jats:p><jats:italic>Short vegetative phase</jats:italic> (<jats:italic>SVP</jats:italic>), a MADS-domain transcription factor, was shown to act as a repressor of flowering in arabidopsis (<jats:italic>Arabidopsis thaliana</jats:italic>). Although the role of <jats:italic>SVP</jats:italic>s in flowering is well characterized in the model plant arabidopsis, little is known in evergreen woody litchi (<jats:italic>Litchi chinensis</jats:italic>). In this study, three litchi <jats:italic>SVP</jats:italic> homologs (<jats:italic>LcSVP1</jats:italic>, <jats:italic>LcSVP2</jats:italic>, and <jats:italic>LcSVP3</jats:italic>) were cloned, and the bioinformatic analysis of the <jats:italic>LcSVP</jats:italic>s was carried out to identify their molecular characteristics. Their expression patterns in the apical meristem (AM) during the transition from vegetative to reproductive phase were studied under natural flowering inductive conditions. Also, brassinosteroid (BR) treatment under low temperature conditions was performed to elucidate the role of <jats:italic>LcSVP</jats:italic>s in the BR-regulated flowering. The results showed that <jats:italic>LcSVP</jats:italic>s belonged to the MADS superfamily. <jats:italic>LcSVP</jats:italic> relative expression levels in AMs of the early- and late-flowering cultivars showed decreasing trends with the transition from vegetative to reproductive growth. Under low temperature condition, relative expression levels of <jats:italic>LcSVP1</jats:italic>, <jats:italic>LcSVP2</jats:italic>, and <jats:italic>LcSVP3</jats:italic> in AMs or panicle primordia showed decreasing trends, whereas those in the AMs of the BR-treated trees remained at relatively high levels. Relative expression analysis of the litchi homolog, <jats:italic>flowering locus t 1</jats:italic> (<jats:italic>LcFT1</jats:italic>), showed that the BR-treated leaves had lower relative expression level than nontreated control leaves. The findings suggest that <jats:italic>LcSVP</jats:italic>s act as repressors involved in flowering in natural conditions and the BR-regulated flowering.</jats:p>

Genome-Wide Identification and Expression Analysis of MADS-Box Family Genes in Litchi (Litchi chinensis Sonn.) and Their Involvement in Floral Sex Determination

“…As an evergreen species in the subtropics, litchi has flowering that is induced by cold temperatures and by GA inhibitors such as uniconazole, paclobutrazol, and daminozide [ 31 , 32 ]. During the cold-dependent floral induction in litchi, the expression of LcSVP homologs decreases in apical meristems and panicle primordia, and this decrease can be alleviated by brassinosteroid treatment [ 33 ]. SVP also interacts with other MADS-box members, such as AP1 and AGAMOUS-LIKE24 (AGL24), to repress floral homeotic genes controlling petal, stamen, and carpel identity [ 34 ].…”

Identification of Chilling Accumulation-Associated Genes for Litchi Flowering by Transcriptome-Based Genome-Wide Association Studies

“…The BR signal transduction components BES1/BZR1 can interact with two proteins, ELF6 (early flowering 6) and its homolog REF6 (relative of early flowering 6) to regulate flowering time in Arabidopsis (Yu et al, 2008). In accordance with the Arabidopsis, litchi flowering was proven to be regulated by ABA (Cui et al, 2013) and BR (Hu et al, 2018). The identified hormone-related CAGs may provide candidate genes for genetic regulation of flowering underlying hormonal control.…”

MIKC type MADS-box transcription factor LcSVP2 is involved in dormancy regulation of the terminal buds in evergreen perennial litchi (Litchi chinensis Sonn.)

“…Hu et al. [ 29 ] later provided indirect evidence showing that all the three LcSVPs identified by Zhang et al. [ 4 ] might serve as flowering repressors in litchi.…”