Flower transcriptional response to long term hot and cold environments in Antirrhinum majus

Abstract

Short term experiments have identified heat shock and cold response elements in many biological systems. However, the effect of long-term low or high temperatures is not well documented. To address this gap, we grew Antirrhinum majus plants from two-weeks old until maturity under control (normal) (22/16°C), cold (15/5°C), and hot (30/23°C) conditions for a period of two years. Flower size, petal anthocyanin content and pollen viability obtained higher values in cold conditions, decreasing in middle and high temperatures. Leaf chlorophyll content was higher in cold conditions and stable in control and hot temperatures, while pedicel length increased under hot conditions. The control conditions were optimal for scent emission and seed production. Scent complexity was low in cold temperatures. The transcriptomic analysis of mature flowers, followed by gene enrichment analysis and CNET plot visualization, showed two groups of genes. One group comprised genes controlling the affected traits, and a second group appeared as long-term adaptation to non-optimal temperatures. These included hypoxia, unsaturated fatty acid metabolism, ribosomal proteins, carboxylic acid, sugar and organic ion transport, or protein folding. We found a differential expression of floral organ identity functions, supporting the flower size data. Pollinator-related traits such as scent and color followed opposite trends, indicating an equilibrium for rendering the organs for pollination attractive under changing climate conditions. Prolonged heat or cold cause structural adaptations in protein synthesis and folding, membrane composition, and transport. Thus, adaptations to cope with non-optimal temperatures occur in basic cellular processes.

Keywords: adaptation; cold stress; floral scent; flower development; heat stress; phenylpropanoid metabolism; ribosomal genes; transcriptome.

Figure 1

Flowering stages of Antirrhinum majus line 165E. Flowering stage range from -IV (before flower opening) until stage V (day 5 after flower opening).

Figure 2

Images of (A) front, (B) back and (C) lateral view of flowers of Antirrhinum majus kept during inflorescence development at low, high and standard temperatures. (D) Flower parameters (P) under standard, high and low temperatures. P1: petal tube length: P2: lower petal length; P3: petal height: P4: sepal length; P5: tube width; P6: upper petal length: P7: lower petal expansion; P8: upper petal expansion: P9: stamen length: P10: gynoecium length: P11: pallate expansion. Different letters for each parameter indicate significant differences according to Fisher's F test or Wilcoxon test (see Supporting Information Table S1 ) (Sepal length and upper petal expansion). (E) PCA of floral weight and flower parameters. Each point represents one of the flowers analyzed. (F) Pedicel length (see Supporting Information Table S2 ).

Figure 3

(A) From left to right, conical cells and (B) flat cells at control, low and, high temperatures. (C) Pollen viability at control (green) low (blue) and high temperature (red), expressed as percentage. (D, E) Total anthocyanin content in petals of Antirrhinum majus flowers grown under control, low, and high temperatures (see Supporting Information Table S3 ). Letters show significant differences between samples.

Figure 4

(A) Total floral scent emitted by flowers. Letters over bars indicate differences across each group (see Supporting Information, Table S5 ) whereas asterisks denote differences across flower stages (see Supporting Information, Table S6 ), (B) Constitutive scent profile of snapdragon flowers under three different conditions (standard, low and high temperatures) and at three development stages, expressed as days after anthesis. This profile comprises those volatiles that were present in all samples from each group. Black and white cells indicate constitutive and non-constitutive compounds, respectively.

Figure 5

CNET plots of Biological Functions with differential regulation. (A) Heat vs control, (B) cold vs control, (C) heat vs cold.

Figure 6

CNET plots of Molecular Functions with differential regulation. (A) Heat vs control, (B) cold vs control, (C) heat vs cold.