Shade delays flowering in Medicago sativa

Abstract

Summary Shade‐intolerant plants respond to the decrease in the red (R) to far‐red (FR) light ratio (R:FR) occurring under shade by elongating stems and petioles and by re‐positioning leaves, in a race to outcompete neighbors for the sunlight resource. In some annual species, the shade avoidance syndrome (SAS) is accompanied by the early induction of flowering. Anticipated flowering is viewed as a strategy to set seeds before the resources become severely limiting. Little is known about the molecular mechanisms of SAS in perennial forage crops like alfalfa (Medicago sativa). To study SAS in alfalfa, we exposed alfalfa plants to simulated shade by supplementing with FR light. Low R:FR light produced a classical SAS, with increased internode and petiole lengths, but unexpectedly also with delayed flowering. To understand the molecular mechanisms involved in uncoupling SAS from early flowering, we used a transcriptomic approach. The SAS is likely to be mediated by increased expression of msPIF3 and msHB2 in low R:FR light. Constitutive expression of these genes in Arabidopsis led to SAS, including early flowering, strongly suggesting that their roles are conserved. Delayed flowering was likely to be mediated by the downregulation of msSPL3, which promotes flowering in both Arabidopsis and alfalfa. Shade‐delayed flowering in alfalfa may be important to extend the vegetative phase under suboptimal light conditions, and thus assure the accumulation of reserves necessary to resume growth after the next season.

Molecular mechanisms underlying phytochrome-controlled morphogenesis in plants

“…A faster transition to flowering by shade cues is common in many crops, but in Medicago sativa , a perennial species, flowering is delayed by additional FR light 8,173 . This suggests that in perennial species, the strategy to survive in suboptimal light environments is to save nutrients for the next season rather than to trigger flowering as in annual species.…”

Light signalling shapes plant–plant interactions in dense canopies

“…In adult Arabidopsis rosette plants, supplemental FR causes petiole and stem elongation (Gommers et al, 2017; Sasidharan et al, 2010). Besides Arabidopsis, supplemental FR elicits internode and stem elongation in stem‐forming plants, such as tobacco, sunflower, soybean, spring wheat, maize, tomato, alfalfa and Powell amaranth (Brainard, Bellinder, & DiTommaso, 2005; Caton, Cope, & Mortimer, 2003; Chitwood et al, 2015; Evers, Andrieu, & Struik, 2006; Green‐Tracewicz, Page, & Swanton, 2011; Lorenzo et al, 2019; Page, Tollenaar, Lee, Lukens, & Swanton, 2009; Wille, Pipper, Rosenqvist, Andersen, & Weiner, 2017). Exposure to low blue light alone does not necessarily cause a change in petiole elongation in Arabidopsis compared to white light, suggesting that petiole elongation is regulated via different pathways or in a different manner in this species as compared to low R:FR‐driven elongation (Pierik, Djakovic‐Petrovic, Keuskamp, de Wit, & Voesenek, 2009), but see Keller et al (2011).…”

Rapid screening and purification of potential inhibitors from Medicago sativa by ultrafiltration‐liquid chromatography combined with stepwise flow rate counter‐current chromatography

“…Medicago sativa is a perennial flowering herbaceous plant of the leguminous family alfalfa, known as the “king of grass” 1 . Medicago sativa contains a variety of flavonoids with antioxidant, stroke, free radical scavenging, anti‐inflammation, trace estrogen‐like effects with potential medicinal value 2 …”