Gibberellin as a factor in floral regulatory networks

Abstract

Gibberellins (GAs) function not only to promote the growth of plant organs, but also to induce phase transitions during development. Their involvement in flower initiation in long-day (LD) and biennial plants is well established and there is growing insight into the mechanisms by which floral induction is achieved. The extent to which GAs mediate the photoperiodic stimulus to flowering in LD plants is, with a few exceptions, less clear. Despite evidence for photoperiod-enhanced GA biosynthesis in leaves of many LD plants, through up-regulation of GA 20-oxidase gene expression, a function for GAs as transmitted signals from leaves to apices in response to LD has been demonstrated only in Lolium species. In Arabidopsis thaliana, as one of four quantitative floral pathways, GA signalling has a relatively minor influence on flowering time in LD, while in SD, in the absence of the photoperiod flowering pathway, the GA pathway assumes a major role and becomes obligatory. Gibberellins promote flowering in Arabidopsis through the activation of genes encoding the floral integrators SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1), LEAFY (LFY), and FLOWERING LOCUS T (FT) in the inflorescence and floral meristems, and in leaves, respectively. Although GA signalling is not required for floral organ specification, it is essential for the normal growth and development of these organs. The sites of GA production and action within flowers, and the signalling pathways involved are beginning to be revealed.

TheFragaria vescaHomolog of SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 Represses Flowering and Promotes Vegetative Growth

“…In Arabidopsis, four major genetic pathways (i.e., the photoperiodic, vernalization, autonomous, and gibberellin [GA] pathways) regulate flowering time (Simpson, 2004;Turck et al, 2008;Kim et al, 2009;Mutasa-Göttgens and Hedden, 2009). Many genes with sequence similarity to known flowering genes are found in different plant families, but their functions may differ between species (Suárez-López et al, 2001;Hayama et al, 2003;Hecht et al, 2005Hecht et al, , 2011Mouhu et al, 2009).…”

Mutation inTERMINAL FLOWER1Reverses the Photoperiodic Requirement for Flowering in the Wild StrawberryFragaria vesca

“…In addition to endogenous cues such as their developmental stage and hormone levels, plants are able to monitor environmental signals, most importantly photoperiod and temperature, for developmental timing (Simpson, 2004;Samach and Wigge, 2005;Turck et al, 2008;Kim et al, 2009;Mutasa-Göttgens and Hedden, 2009). Appropriate developmental timing is especially important for perennial species, which may live for many years, undergoing repeated cycles of vegetative and reproductive (flowering) development, which are regulated by changes in the seasons through the year.…”

TEMPRANILLO genes link photoperiod and gibberellin pathways to control flowering in Arabidopsis

“…In addition, results from the short days (SD)-LD shift experiment suggest that TEM genes are differentially expressed in SD and LD, and their prompt downregulation upon day-time extension may account for the upregulation of FT in increasing day length. Under SD, signalling downstream gibberellin (GA) perception is critical for flowering 7 , as GA accumulation induces SOC1 and LEAFY (LFY) expression in the SAM 8,9 . However, the mechanism responsible for the rise in GA levels that ultimately triggers flowering under SD is largely unknown.…”