New Arabidopsis Recombinant Inbred Lines (Landsberg erecta × Nossen) Reveal Natural Variation in Phytochrome-Mediated Responses

Abstract

We used 52 Arabidopsis (Arabidopsis thaliana) accessions and developed a new set of 137 recombinant inbred lines between Landsberg erecta (Ler) and to explore the genetic basis of phytochrome-mediated responses during deetiolation. Unexpectedly, most accessions showed weak or moderate hypocotyl growth and cotyledon unfolding responses to pulses of far-red light (FR). Crosses between Columbia and No-0, two accessions with poor response, segregated seedlings with unfolded cotyledons under pulsed FR, suggesting the occurrence of accession-specific loci in the repression of morphological responses to weak light signals. Confirming the latter expectation, mapping of responses to pulsed FR in the Ler 3 No-0 lines identified novel loci. Despite its weak response to pulsed FR, No-0 showed a response to continuous FR stronger than that observed in Ler. By mapping the differential effect of pulsed versus continuous FR, we identified two high-irradiance response loci that account for the steeper response to continuous FR in No-0. This underscores the potential of the methodology to identify loci involved in the regulation of the shape of signal input-output relationships. Loci specific for a given phytochromemediated response were more frequent than pleiotropic loci. Segregation of these specific loci is predicted to yield different combinations of seedling responsivity to light. Such flexibility in combination of responses is observed among accessions and could aid in the adjustment to different microenvironments.Some fluctuations of the light environment tightly correlate with the occurrence of conditions that impose a challenge to plant survival such as seasonal changes that result in extreme temperatures, organ emergence out of the soil, or competition with neighbor individuals. Subtle light signals, including small changes in photoperiod throughout the year, the transition between darkness and very low fluences of light reaching the top millimeters of the soil, and small reductions in the red light (R) to far-red light (FR) ratio caused by light reflected by neighbors, actually anticipate stressful conditions. Plants are able to perceive these signals, which are translated into regulation of developmental plasticity (Casal et al., 2004). Not surprisingly, fitting developmental decisions to these signals requires an intricate network of molecular players.The use of Arabidopsis (Arabidopsis thaliana) mutants has been the primary approach in the search for players in light signaling. Mutant screens have led to the discovery of the photoreceptors phytochrome A (phyA; Whitelam et al., 1993), phytochrome B (phyB; Koornneef et al., 1980;Reed et al., 1993), cryptochrome 1 (Koornneef et al., 1980;Ahmad and Cashmore, 1993), and cryptochrome 2 (cry2; Koornneef et al., 1980;Guo et al., 1998). However, a complementary approach to mutant analysis has been the exploration of natural allelic variation. The use of recombinant inbred lines (RILs) between the accessions Landsberg erecta (Ler) and Cape Verde Islands (Cvi) helped to iden...

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“…, 2004), Bay‐0 × Sha‐0 (Loudet et al. , 2002), Col‐4 × Laer‐0 (Lister and Dean, 1993) and Laer‐0 × No‐0 (Magliano et al. , 2005) (Figure 5 and data not shown).…”

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“…Fig 3 shows that expression of this protein does not cause a dominant negative effect under FR. To assess the activities of the tagged phyAs in signaling through the VLFR, lines were grown under hourly pulses of FR [ 39 , 40 ]. Fig 4A shows that all the myc-tagged phyAs mediate a robust VLFR, whereas the 35S:phyA-YFP fusion is not active in VLFR.…”

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“…Most of the accessions show a weak response to FR pulses and the two traits are not correlated. Forty accessions among 52 showed reduced cotyledons unfolding suggesting that this character is commonly repressed in populations [ 62 ].…”