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Research Teams Identify Two microRNAs Involved in Perennial Flowering

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Two new studies were published this week linking two microRNAs to the flowering of different perennial plants.

Perennials live for many years, and much control the time and duration of flowering in order to maintain the resources needed for multiple flowering cycles. Notably, older plants flower in response to environmental signals, whereas younger ones remain dormant despite such triggers.

To understand how increasing age and exposure to winter cold, or vernalization, work together to establish competence to flower, a group from the Max Planck Institute for Plant Breeding Research examined Arabis alpine, a relative of Arabidopsis thaliana.

They found that the transcription factor APETALA2, which is a target of miR-172, prevents flowering prior to vernalization. Additionally, levels of another miRNA, miR-156, decrease as the plant ages, which increase production of so-called SPL transcription factors to ensure that flowering occurs in response to cold. Notably, the age at which Arabis alpine begins to respond to vernalization can be changed by manipulating levels of miR-156.

Although the two miRNAs’ levels are uncoupled in the plant, “miR-156 abundance represents the timer controlling age-dependent flowering responses to cold,” the researchers wrote.

In a separate study, an international team led by investigators from the Shanghai Institutes for Biological Sciences focused on Cardamine flexuosa, a herbaceous biennial-to-perennial plant that also requires vernalization to flower.

They found that levels of both miR-172 and miR-156 are necessary to regulate the timing of sensitivity in response to vernalization.

“We suggest that age and vernalization cues coordinate to regulate floral induction in C. flexuosa by removal of two repressors, CfFLC, which is repressed by vernalization, and CfTOE1, which is downregulated by” miR-156 through its effect on SPL transcription factors, the team wrote in its paper.

“In the young seedling, high levels of miR156 lead to the accumulation of CfTOE1,” which represses CfSOC1 expression regardless of vernalization,” it added. “As the plant grows, the endogenous sugar content is elevated, resulting in a decreased level of miR156 and the concomitant increase in miR172.”

Both papers appeared in this week's Science.

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