Extensive phenotypic variation in early flowering mutants of Arabidopsis

Abstract

Flowering time, the major regulatory transition of plant sequential development, is modulated by multiple endogenous and environmental factors. By phenotypic profiling of 80 early flowering mutants of Arabidopsis, we examine how mutational reduction of floral repression is associated with changes in phenotypic plasticity and stability. Flowering time measurements in mutants reveal deviations from the linear relationship between the number of leaves and number of days to bolting described for natural accessions and late flowering mutants. The deviations correspond to relative early bolting and relative late bolting phenotypes. Only a minority of mutants presents no detectable phenotypic variation. Mutants are characterized by a broad release of morphological pleiotropy under short days, with leaf characters being most variable. They also exhibit changes in phenotypic plasticity across environments for florigenic-related responses, including the reaction to light and dark, photoperiodic behavior, and Suc sensitivity. Morphological pleiotropy and plasticity modifications are differentially distributed among mutants, resulting in a large diversity of multiple phenotypic changes. The pleiotropic effects observed may indicate that floral repression defects are linked to global developmental perturbations. This first, to our knowledge, extensive characterization of phenotypic variation in early flowering mutants correlates with the reports that most factors recruited in floral repression at the molecular genetic level correspond to ubiquitous regulators. We discuss the importance of functional ubiquity for floral repression with respect to robustness and flexibility of network biological systems.

Figure 1.

Variation in the RPF in SD. Relation between the number of rosette leaves and the number of days to bolting for eav1 to eav61 T-DNA insertion mutants (blue diamonds), eav62 to eav80 EMS mutants (yellow diamonds), ebv1 (green square), and the Ws (red circles) and Col-0 (black circles) ecotypes. Independent repeats are presented (2 on average for eav1 to eav61 and 12 for Ws). sds are shown for Ws and Col-0 only for the sake of clarity. Thin line: linear regression for the population of T-DNA insertion mutants. Dotted red line: linear regression calculated with Ws and Col-0 (out of scale: average 66.2 rosette leaves and 61.3 d to bolting) scores. Area between black dotted lines: range of variation of wild-type relative RPF.

Figure 2.

Morphological pleiotropy of early flowering mutants in SD. A, Ws, rosette and base of the floral stem showing the first cauline leaf. B, eav2. C, eav6. D, eav43. E, eav1. F, eav15. G, eav49. H, eav40. I, ebv1. J, Variation of morphological pleiotropy (proportion of modified parameters in 28 variable morphological parameters) with flowering time in T-DNA insertion mutants (diamonds) and Ws (black circles). sds are shown for 12 Ws independent repeats. Thin line: linear regression.

Figure 3.

Variability of morphological pleiotropy in early flowering mutants under SD. A, Distribution of morphological changes in eav1 to eav61 T-DNA insertion mutants. Empty and filled boxes indicate, respectively, the absence and presence of macroscopically detectable morphological changes. B, Frequency of changes in 28 morphological parameters. Elongation of hypocotyl (1) and petiole (2). Rosette size (3), raising (4), and pigmentation (5). Rosette leaf shape (6), serration (7), surface (8), and trichomes (9). Cauline leaf size (10), shape (11), serration (12), and surface (13). Flower size (14) and number (15). Perianth organ shape (16) and reproductive organ shape (17). Silique size (18), shape (19), and fertility (20). Floral stem elongation (21), length of first internode (22), length of other internodes (23), thickness (24), and appendage arrangement (25). Coflorescence elongation (26), number of secondary inflorescence (27), and secondary inflorescence elongation (28).

Figure 4.

Response to photoperiod. Flowering time under SD (shaded bars) and LD (white bars) in eav T-DNA insertion mutants (numbered from 1–61) grouped in four different classes based on t test scores: PhP1 (later in LD than in SD), PhP2 (insensitive to photoperiod), PhP3 (early in SD and in LD), PhP4 (early specifically in SD). The Ws control is shown on both rows (average of 12 and 9 repeats in SD and LD, respectively). sds are indicated.

Figure 5.

Norms of reaction to light and dark, photoperiod, and Suc. A–B, Hypocotyl elongation in LD (black bars), in SD (red bars) and in the dark (blue bars) in eav T-DNA insertion mutants (numbered from 1–61) and in Ws (average of 17 repeats in LD, 8 in SD, and 12 in the dark). Error bars correspond to sds. A, Classes of mutants differing from Ws in the light (Hyp1, Hyp3) or in the dark (Hyp5), or both (Hyp2, Hyp4) based on t test scores. B, Mutants similar to Ws in the light and in the dark (HypN). Corresponding reactions to photoperiod (classes PhP1 to 4) or to 6% Suc (classes Suc1 to N) are indicated. C, Combined changes in photoperiod response (P), Suc sensitivity (S), and hypocotyl elongation (H), or absence of changes (+).

Figure 6.

Variation of phenotypic plasticity with flowering time in eav1 to eav61 T-DNA insertion mutants (diamonds) and Ws (black circles), showing the tendency of the different norms of reaction. A, Response to 6% Suc, classes Suc1 to 3 (brown diamonds), class SucN (white diamonds). B, Response to photoperiod, classes PhP1 to 2 (green diamonds), class PhP3 (red diamonds), class PhP4 (white diamonds). C, Hypocotyl elongation in response to light and dark, class Hyp1 (blue diamonds), class Hyp2 (indigo diamonds), classes Hyp3 to 4 (red crosses), class Hyp5 (yellow diamonds), class HypN (white diamonds). Plasticity index (Pi; see “Materials and Methods”). Thin line: linear regression. sds are shown for 12 Ws independent repeats.