BIANNUALREPORT2012-2013

New clues about the mechanism that inhibits early flowering in plants

Flowering is controlled by several genetic mechanisms that respond to external stimuli. Those stimuli include the hours of light or length of day (photoperiod). The vast majority of plants flower and set fruits between spring and summer, when days are longer. Indeed, plants are capable of “differentiating” between those favorable conditions, long days, and unfavorable conditions, short days as in winter, and to respond accordingly by activating the appropriate mechanism.

FT protein is the main promoter of flowering when days are long, and it was known that FT is inhibited by the TEMPRANILLO genes, delaying flowering. It was also known that when days are unexpectedly shorter – what would happen, for example, if the plant is moved from one country to another and at the time of flowering, the plant finds fewer hours of light – the FT protein does not act, despite that plants need to bloom to perpetuate. In this case, plants have an “auxiliary” mechanism: it is the accumulation of phytohormones, gibberellins, which triggers flowering. However, the mechanisms involved in the regulation of the accumulation of these hormones remained unknown.

The team led by ICREA Research Professor Soraya Pelaz found that it is the same TEM genes which inhibit the synthesis of gibberellins. The results show that TEMPRANILLO genes control flowering both in unfavorable (short days) and favorable conditions (long days). Therefore, by modulating TEM activity, flowering can be directly controlled in both day-length conditions.

Researchers demonstrated that modified Arabidopsis plants that overexpress TEM are deficient in gibberellins, so they fail to flower. However, if external gibberellins are added, the plant re-establish flowering at a normal time. Conversely, mutant plants that do not express TEM genes, bloom earlier than normal plants.

Therefore, TEM genes play a key role inhibiting flowering if days are long or short. TEM genes affect both genetic pathways controlling flowering in different environmental conditions. Under adverse conditions, flowering is delayed to achieve the proper time for seed set. Even in favorable conditions, bloom must be adequately postponed for the plant to acquire the necessary reserves for flower and fruit formation. In both cases TEM avoids a precocious flowering.

TEM genes and their function were first discovered in 2008 by the same research team.  Since then, TEM genes are being isolated and identified in numerous species, suggesting that this way of controlling flowering time is general to many plant species.