Shade delays flowering in Medicago sativa

ALONSO ISERTE, JAVIER; GARCIA GAGLIARDI, PEDRO; VAZQUEZ, MARTIN; CERDÁN, PABLO D.; LORENZO, CHRISTIAN D.; ANTONIETTI, MARIANA SOFIA; DEZAR, CARLOS ALBERTO A.; YANOVSKY, MARCELO J.; SANCHEZ LAMAS, MAXIMILIANO; HERNANDO, CARLOS E.; CASAL, JORGE J.

PLANT JOURNAL

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2019 vol. 99 p. 7 - 22

0960-7412

Shade-intolerant plants respond to the decrease in the red (R) to far-red (FR) light ratio (R:FR) occurringunder shade by elongating stems and petioles and by re-positioning leaves, in a race to outcompete neigh-bors for the sunlight resource. In some annual species, the shade avoidance syndrome (SAS) is accompa-nied by the early induction of flowering. Anticipated flowering is viewed as a strategy to set seeds beforethe resources become severely limiting. Little is known about the molecular mechanisms of SAS in peren-nial forage crops like alfalfa (Medicago sativa). To study SAS in alfalfa, we exposed alfalfa plants to simu-lated shade by supplementing with FR light. Low R:FR light produced a classical SAS, with increasedinternode and petiole lengths, but unexpectedly also with delayed flowering. To understand the molecularmechanisms involved in uncoupling SAS from early flowering, we used a transcriptomic approach. The SASis likely to be mediated by increased expression of msPIF3 and msHB2 in low R:FR light. Constitutiveexpression of these genes in Arabidopsis led to SAS, including early flowering, strongly suggesting thattheir 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 impor-tant to extend the vegetative phase under suboptimal light conditions, and thus assure the accumulation ofreserves necessary to resume growth after the next season.