A Novel Role for Banana MaASR in the Regulation of Flowering Time in Transgenic Arabidopsis

Abstract

The abscisic acid (ABA)-, stress-, and ripening-induced (ASR) protein is a plant-specific hydrophilic transcriptional factor involved in fruit ripening and the abiotic stress response. To date, there have been no studies on the role of ASR genes in delayed flowering time. Here, we found that the ASR from banana, designated as MaASR, was preferentially expressed in the banana female flowers from the eighth, fourth, and first cluster of the inflorescence. MaASR transgenic lines (L14 and L38) had a clear delayed-flowering phenotype. The number of rosette leaves, sepals, and pedicel trichomes in L14 and L38 was greater than in the wild type (WT) under long day (LD) conditions. The period of buds, mid-flowers, and full bloom of L14 and L38 appeared later than the WT. cDNA microarray and quantitative real-time PCR (qRT-PCR) analyses revealed that overexpression of MaASR delays flowering through reduced expression of several genes, including photoperiod pathway genes, vernalization pathway genes, gibberellic acid pathway genes, and floral integrator genes, under short days (SD) for 28 d (from vegetative to reproductive transition stage); however, the expression of the autonomous pathway genes was not affected. This study provides the first evidence of a role for ASR genes in delayed flowering time in plants.

Fig 1. Expression of MaASR gene in banana female flowers from the upper inflorescence.

(A) The female flowers from the tenth (F10), ninth (F9), eighth (F8), fourth (F4), and first (F1) cluster from the upper inflorescence. (B) Relative expression level in banana female flowers. The y-axis represents the relative fold-difference in mRNA level, which was calculated using the 2^-ΔΔCT formula with ACTIN and UBQ as internal controls. The vertical bars represent the mean ± SD of three replicates.

Fig 2. Flowering phenotypes of MaASR transgenic plants.

(A) Phenotype of floral organs detached from the same position and developmental stage of 14 d under LD in WT and transgenic plants. (B) Plants at 14 d under LD. (C) Flowering days of MaASR transgenic lines L14 and L38. (D) The number of rosette leaves of MaASR transgenic lines L14 and L38. (E) Plants at 28 d under LD. (F) The number of plants at flower buds stage. (G) The number of plants at mid-flower stage. (H) The number of plants at full-bloom stage.

Fig 3. TreeView representation of ESTs from microarray data (L14 vs WT) and functional classification of flowering-related candidate genes.

(A) Gene expression profile of transgenic plants L14 and WT. (B) Functional classification of candidate genes. Red: up-regulated genes; Green: down-regulated genes.

Fig 4. Expression analysis of photoperiod pathway genes, vernalization pathway genes, flower development related genes, GA pathway genes, floral integrator genes, and autonomous pathway genes in WT and MaASR transgenic plants.

(A) Photoperiod pathway genes. (B) Vernalization pathway genes. (C) Flower development related genes. (D) GA pathway genes. (E) Floral integrator genes. (F) Autonomous pathway genes. WT: Wild-type; L14, L38: MaASR transgenic lines. Data are represented as mean ± SD of biological replicates (n = 3). Means denoted by the same letter do not significantly differ when set at P<0.05 as determined by Duncan’s multiple range tests.

Fig 5. A tentative model showing the main genes involved in the multiple flowering pathway in MaASR overexpressed plants.