MsTFL1A delays flowering and regulates shoot architecture and root development in Medicago sativa.

KEY MESSAGE: MsTFL1A is an important gene involved in flowering repression in alfalfa (Medicago sativa) which conditions not only above-ground plant shoot architecture but also root development and growth. Delayed flowering is an important trait for forage species, as it allows harvesting of high-quality forage for a longer time before nutritional values decline due to plant architecture changes related to flowering onset. Despite the relevance of delayed flowering, this trait has not yet been thoroughly exploited in alfalfa. This is mainly due to its complex genetics, sensitivity to inbreeding and to the fact that delayed flowering would be only advantageous if it allowed increased forage quality without compromising seed production. To develop new delayed-flowering varieties, we have characterized the three TERMINAL FLOWERING 1 (TFL1) family of genes in alfalfa: MsTFL1A, MsTFL1B and MsTFL1C. Constitutive expression of MsTFL1A in Arabidopsis caused late flowering and changes in inflorescence architecture, indicating that MsTFL1A is the ortholog of Arabidopsis TFL1. Overexpression of MsTFL1A in alfalfa consistently led to delayed flowering in both controlled and natural field conditions, coupled to an increase in leaf/stem ratio, a common indicator of forage quality. Additionally, overexpression of MsTFL1A reduced root development, reinforcing the role of MsTFL1A not only as a flowering repressor but also as a regulator of root development.We conclude that the precise manipulation of MsTFL1A gene expression may represent a powerful tool to improve alfalfa forage quality.

Improvement of alfalfa forage quality and management through the down-regulation of MsFTa1.

Alfalfa (Medicago sativa L.) is one of the most important forage crops worldwide. As a perennial, alfalfa is cut several times each year. Farmers face a dilemma: if cut earlier, forage nutritive value is much higher but regrowth is affected and the longevity of the stand is severely compromised. On the other hand, if alfalfa is cut later at full flower, stands persist longer and more biomass may be harvested, but the nutritive value diminishes. Alfalfa is a strict long-day plant. We reasoned that by manipulating the response to photoperiod, we could delay flowering to improve forage quality and widen each harvesting window, facilitating management. With this aim, we functionally characterized the FLOWERING LOCUS T family of genes, represented by five members: MsFTa1, MsFTa2, MsFTb1, MsFTb2 and MsFTc. The expression of MsFTa1 correlated with photoperiodic flowering and its down-regulation led to severe delayed flowering. Altogether, with late flowering, low expression of MsFTa1 led to changes in plant architecture resulting in increased leaf to stem biomass ratios and forage digestibility. By manipulating photoperiodic flowering, we were able to improve the quality of alfalfa forage and management, which may allow farmers to cut alfalfa of high nutritive value without compromising stand persistence.

Emerging Hubs in Plant Light and Temperature Signaling.

Due to their nature as sessile organisms, plants must accurately sense their surroundings and then translate this information into efficient acclimation responses to maximize development. Light and temperature are two major stimuli that provide immediate cues regarding energy availability, daylength, proximity of other species and seasonal changes. Both cues are sensed by complex systems and the integration of these signals is of very high value to properly respond to environmental changes without being disguised by random changes. For instance a cold day has a different significance if it occurs during the illuminated phase of the day or during the night, or when days are shortening during the fall instead of a long-day in spring. Here, we summarize recent advances in the nature of signaling components that operate as connectors of light and temperature signaling, with emphasis on the emerging hubs. Despite the nature of the thermosensors is still in its infancy compared to an important body of knowledge about plant sensory photoreceptors, the interaction of both types of signaling will not only bring clues of how plants integrate environmental information, but also will help in leading research in the nature of the thermosensors themselves.