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First published online July 27, 2006

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Flowering: the hows and whens

Two papers in this issue discuss flowering - one addresses its timing, and the other the specification of flower organ identity. On p. 3213, Hoecker and colleagues have investigated how the SPA protein family helps plants to adjust their development to the environment. The researchers have previously shown that SPA proteins are required for skotomorphogenesis (the growth that occurs when seedlings are kept in the dark); now they investigate the role of SPA proteins in photoperiodic flowering (the timing of flowering in response to day length). They show that all four SPA proteins interact with CONSTANS (CO), which is essential for the early flowering that occurs in response to long days. CO transcription is regulated by the circadian clock and its protein is stabilised by light, which together allow CO protein to accumulate only when days are long. The presence of high levels of CO protein in spa triple mutants lead the authors to speculate that SPA proteins control the stability of CO in response to light.

The mechanisms by which floral organs develop are largely well characterised - A, B, C and E class genes combine to direct the development of the four floral whorls into stamens, carpals, petals and sepals - but some crucial aspects remain unclear. On p. 3159, Liu and colleagues describe a new model for the regulation of the class C gene AGAMOUS (AG), which specifies stamen and carpel development in the inner two whorls. The researchers previously identified two transcriptional co-repressors called SEUSS (SEU) and LEUNIG (LUG) that prevent ectopic expression of AG. The authors now show that these co-repressors interact with the MADs box proteins SEPALLATA3 (SEP3) and APETALA1 (AP1), converting them from activators into repressors of AG expression. So although previous models hold that AG is activated in all four whorls and repressed in the outer two, these researchers suggest that SEU and LUG repress AG in all four whorls, but that this is then antagonised by AG activation in the inner whorls.

Related articles in Development:

APETALA1 and SEPALLATA3 interact with SEUSS to mediate transcription repression during flower development

Vaniyambadi V. Sridhar, Anandkumar Surendrarao, and Zhongchi Liu
Development 2006 133: 3159-3166. [Abstract] [Full Text]  

Arabidopsis SPA proteins regulate photoperiodic flowering and interact with the floral inducer CONSTANS to regulate its stability

Sascha Laubinger, Virginie Marchal, José Gentilhomme, Stephan Wenkel, Jessika Adrian, Seonghoe Jang, Carmen Kulajta, Helen Braun, George Coupland, and Ute Hoecker
Development 2006 133: 3213-3222. [Abstract] [Full Text]  

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Related articles in Development Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Search for Related Content