Characterization of Shade Avoidance Responses inLotus japonicus

Abstract

Sessile plants must continuously adjust their growth and development to optimize photosynthetic activity under ever-fluctuating light conditions. Among such light responses in plants, one of the best-characterized events is the so-called shade avoidance, for which a low ratio of the red (R):far-red (FR) light intensities is the most prominent stimulus. Such shade avoidance responses enable plants to overtop their neighbors, thereby enhancing fitness and competitiveness in their natural habitat. Considerable progress has been achieved during the last decade in understanding the molecular mechanisms underlying the shade avoidance responses in the model rosette plant, Arabidopsis thaliana. We characterize here the fundamental aspects of the shade avoidance responses in the model legume, Lotus japonicus, based on the fact that its phyllotaxis (or morphological architecture) is quite different from that of A. thaliana. It was found that L. japonicus displays the characteristic shade avoidance syndrome (SAS) under defined laboratory conditions (a low R:FR ratio, low light intensity, and low blue light intensity) that mimic the natural canopy. In particular, the outgrowth of axillary buds (i.e., both aerial and cotyledonary shoot branching) was severely inhibited in L. japonicus grown in the shade. These results are discussed with special emphasis on the unique aspects of SAS observed with this legume.

Flowering and Growth Responses of Cultivated Lentil and Wild Lens Germplasm toward the Differences in Red to Far-Red Ratio and Photosynthetically Active Radiation

“…Genetically distinct signaling pathway segments among the phytochrome family members were also identified (Li et al, 2011). Various studies report that phytochrome genes and flowering genes are well-conserved between Arabidopsis and legumes at the level of sequence and physiological function (Hecht et al, 2005; Ueoka-Nakanishi et al, 2011; Wu et al, 2011). Therefore, we suspect that differences in genes of the red and far-red light absorbing phytochrome family and its signaling pathway may also play a direct and important role with respect to the different flowering responses within Lens genotypes.…”

Molecular control of crop shade avoidance

“…Auxin has also been shown to be a key regulator of the SAR in the model legume species, Lotus japonicus. Not only does L. japonicus display several of the classical shade avoidance syndromes including elongated internodes, early flowering, and reduction in lateral branching, but homologs of known SAR auxin regulatory factors, an Arabidopsis homeobox domain-containing transcription factor, ATHB2, and IAA29, are upregulated under shade [32,[68][69][70].…”

Arabidopsis HD-Zip II proteins regulate the exit from proliferation during leaf development in canopy shade

“…Elevated levels of HAT1 , HAT2 , HAT3 , and ATHB4 result in phenotypes analogous to those caused by ATHB2 overexpression ( Sawa et al , 2002 ; Ciarbelli et al , 2008 ; Sorin et al , 2009 ; Ruberti et al , 2012 ; Ruzza et al , 2014 ), further indicating a redundant function of these transcription factors in shade avoidance. Interestingly, homologue genes have been found to be up-regulated in monocotyledonous and dicotyledonous plants exposed to low R/FR light, suggesting a conserved function of HD-Zip II transcription factors through evolution ( Ueoka-Nakanishi et al , 2011 ; Chitwood et al , 2015 ; Wang et al , 2016 ).…”