Abstract
Flowering of many plants is induced by environmental signals, but these responses can depend on the age of the plant. Exposure of Arabidopsis thaliana to vernalization (winter temperatures) at germination induces flowering, whereas a close perennial relative Arabis alpina only responds if exposed when at least 5 weeks old. We show that vernalization of these older A. alpina plants reduces expression of the floral repressor PEP1 and activates the orthologs of the Arabidopsis flowering genes SOC1 (Aa SOC1) and LFY (Aa LFY). By contrast, when younger plants are vernalized, PEP1 and Aa SOC1 mRNA levels change as in older plants, but Aa LFY is not expressed. We demonstrate that A. alpina TFL1 (Aa TFL1) blocks flowering and prevents Aa LFY expression when young plants are exposed to vernalization. In addition, in older plants, Aa TFL1 increases the duration of vernalization required for Aa LFY expression and flowering. Aa TFL1 has similar functions in axillary shoots, thus ensuring that following a flowering episode vegetative branches are maintained to continue the perennial life cycle. We propose that Aa TFL1 blocks flowering of young plants exposed to vernalization by setting a threshold for a flowering pathway that is increased in activity as the shoot ages, thus contributing to several perennial traits.
Highlights
Flowering is controlled by interactions between regulatory networks that control shoot development and those that mediate responses to the environment
35S:Aa TFL1dsRNAi plants were determinate, ending in a terminal flower, in contrast with the indeterminate development of wild-type A. alpina Pajares (Figure 4B). These results indicated that alpina TERMINAL FLOWER1 (TFL1) (Aa TFL1) does not contribute to the obligate vernalization requirement of A. alpina Pajares plants but that reducing Aa TFL1 expression causes slightly earlier flowering after vernalization
At TFL1 contributes to the extreme late flowering conferred by FRI FLOWERING LOCUS C (FLC), but in the absence of At TFL1 activity, FRI FLC plants were still very late flowering. These results indicate that Aa TFL1 is not required for the absolute block on flowering before vernalization in A. alpina Pajares, while in Arabidopsis, TFL1 makes a small contribution to the delay in flowering of FLC FRI plants before vernalization
Summary
Flowering is controlled by interactions between regulatory networks that control shoot development and those that mediate responses to the environment. These processes are most thoroughly understood in Arabidopsis thaliana, where six pathways have been described to regulate flowering in response to environmental or developmental cues (Fornara et al, 2010). Flowering of many plant species is more sensitive to environmental cues as the plant ages (Hackett, 1985). This increasing sensitivity to the environment is prevalent in perennials.
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