Grasses suppress shoot-borne roots to conserve water during drought
Thursday, 2016/08/04 | 08:24:08
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Jose Sebastian, Muh-Ching Yee, Willian Goudinho Viana, Rubén Rellán-Álvarez, Max Feldman, Henry D. Priest, Charlotte Trontin, Tak Lee, Hui Jiang, Ivan Baxter, Todd C. Mockler, Frank Hochholdinger, Thomas P. Brutnell, and José R. Dinneny SignificanceGrasses, whose members constitute key food and bioenergy crops worldwide, use unique developmental programs to establish the root system from the shoot. Shoot-borne crown roots originate near the soil surface and provide the main conduits through which the plant takes up water and nutrients. We show that crown root development is the major target of drought stress signaling. Water deficit-triggered crown root arrest provides an important mechanism to conserve water under drought, and this response is widely conserved across grass species. Substantial phenotypic variation exists in maize for this trait, which may be a useful target in breeding efforts to improve drought tolerance. AbstractMany important crops are members of the Poaceae family, which develop root systems characterized by a high degree of root initiation from the belowground basal nodes of the shoot, termed the crown. Although this postembryonic shoot-borne root system represents the major conduit for water uptake, little is known about the effect of water availability on its development. Here we demonstrate that in the model C4 grass Setaria viridis, the crown locally senses water availability and suppresses postemergence crown root growth under a water deficit. This response was observed in field and growth room environments and in all grass species tested. Luminescence-based imaging of root systems grown in soil-like media revealed a shift in root growth from crown-derived to primary root-derived branches, suggesting that primary root-dominated architecture can be induced in S. viridis under certain stress conditions. Crown roots of Zea mays and Setaria italica, domesticated relatives of teosinte and S. viridis, respectively, show reduced sensitivity to water deficit, suggesting that this response might have been influenced by human selection. Enhanced water status of maize mutants lacking crown roots suggests that under a water deficit, stronger suppression of crown roots actually may benefit crop productivity.
See: http://www.pnas.org/content/113/31/8861.abstract.html?etoc PNAS August 2, 2016; vol.113; no.31: 8861–8866
Fig. 1. Crown root growth is suppressed in S. viridis as a response to WD. (A) Comparison of whole-root systems of S. viridis grown under WW and WD conditions (30 DAS). (B) Comparison of crown regions of WW- and WD-treated S. viridis plants (25 DAS). (C) Magnified image of WD-treated S. viridis crown region showing the presence of arrested crown roots. (D) Comparison of plant dry weight under WW and WD conditions (34 DAS; n = 15–20 plants per condition). (E) Number of arrested and outgrown crown roots under WW and WD conditions (41 DAS; n = 10–15 plants per condition). (F) Crown root response to WD treatment in 18 S. viridis accessions (40 DAS; n = 5–10 plants per accession). (G) Number of leaves and crown roots quantified in field-grown plants under WW and WD conditions. Data are an average of results from six subplot replicates (n = 120–130 plants per treatment). (H) Time-lapse images of the crown region of a WD-treated plant after rewatering. Labels indicate time after rewatering. Image series shows rapid emergence and elongation of new roots from the crown, whereas previously emerged roots remain arrested. (I) Quantification of outgrown and arrested crown root formation in plants grown under WW (Left), WD (Center), or WD followed by rewatering (Rewatered, Right) (n = 25 plants). Plants in the rewatered condition were WD-treated until the 14th DAS and then rewatered. (Scale bars: 1 cm in A and B, 1.5 mm in C and H.) *P < 0.05, Student’s t test. Error bars represent SE. |
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