Autonomous, environmental and exogenous gibberellin regulation of floral development and isolation of a putative partial FLORICAULA/LEAFY homologue in Phormium cookianum (Agavaceae)

Abstract

Competence to flower, floral induction, and expression of a putative partial homologue of the FLORICAULA/LEAFY (FLO/LFY) in the monocarpic perennial Phormium cookianum (Agavaceae) were studied in response to environmental manipulation and application of gibberellic acid (GA3). Floral induction was unaffected by temperature or daylength. The absence of flowering seen in half of the P. cookianum plants was associated with a small fan size. Application of GA3 followed by growth under cold/short day conditions increased the proportion of plants flowering and advanced the attainment of competence to flower in smaller fans. A fragment of the putative homologue of FLO/LFY in P. cookianum (PFL) showed strong sequence similarity to other FLO/LFY-like genes. PFL mRNA expression was quantified using real-time reverse transcriptase-PCR. Up-regulation of PFL in the region of the shoot apical meristem occurred over time, and increases coincided with the transition from vegetative to inflorescence development. Greater PFL expression was observed in fans of larger size, these being the fans with greater likelihood of flowering. Application of GA3 accelerated the rise in PFL expression, but level of expression of PFL did not correlate with the increased proportion of plants flowering.