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Title: Grasses suppress shoot-borne roots to conserve water during drought

Author
item SEBASTIAN, JOSE - Carnegie Institute - Stanford
item YEE, MUH-CHING - Carnegie Institute - Stanford
item VIANA, WILLIAN - Carnegie Institute - Stanford
item RELLAN-ALVAREZ, RUBEN - Centro De Investigacion
item FELDMAN, MAX - Danforth Plant Science Center
item PRIEST, HENRY - Danforth Plant Science Center
item TRONTIN, CHARLOTTE - Carnegie Institute - Stanford
item LEE, TAK - Yonsei University
item JIANG, HUI - Danforth Plant Science Center
item Baxter, Ivan
item MOCKLER, TODD - Danforth Plant Science Center
item HOCHHOLDINGER, FRANK - University Of Bonn
item BRUTNELL, THOMAS - Danforth Plant Science Center
item DINNENY, JOSE - Carnegie Institute - Stanford

Submitted to: Proceedings of the National Academy of Sciences (PNAS)
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/2/2016
Publication Date: 8/2/2016
Citation: Sebastian, J., Yee, M., Viana, W.G., Rellan-Alvarez, R., Feldman, M., Priest, H., Trontin, C., Lee, T., Jiang, H., Baxter, I.R., Mockler, T., Hochholdinger, F., Brutnell, T.P., Dinneny, J.R. 2016. Grasses suppress shoot-borne roots to conserve water during drought. Proceedings of the National Academy of Sciences. 113(31):8861-8866. doi: 10.1073/pnas.1604021113.

Interpretive Summary: Crops from the Poaceae, including Maize, Sorghum and Sugarcane, develop roots from nodes on the stem above the seed, and frequently above the soil, termed crown roots. These roots are very important for bringin water to the shoot, but little is known about how the availability or lack of water effects their devleopment. Here we used a model plant that is closely related to these crops, Setaria viridis (green millett) to study the crown root response to water deficit. In response to water deficit in the immediate vicinity of of the node, the growth from the roots is suppressed. Using plants with a luminscent reporter, we were able to demonstrate that the plants shift resources to the primary root when crown root growth is inhibited. The same response was observed in a range of grass species, although domesticated plants showed reduced sensistivity of crown root growth to water deficit, suggesting that human selection may have effected this trait. These results will improve our understanding of this important process in grasses and understanding the results on the molecular level could help make a wide variety of crops, such as non-grasses soybean and cotton, more drought tolerant.

Technical Abstract: Many important crops are members of the Poaceae family, and develop fibrous root systems characterized by a high-degree of root initiation from the basal nodes of the shoot, termed the crown. While this post-embryonic shoot-borne root system represents the major conduit for water uptake, little is known regarding what effect water availability has on its development. Here we demonstrate that in the model C4 grass Setaria viridis, the crown locally senses water availability and suppresses post-emergence crown root growth under water deficit. This response was observed in field and growth room environments and in all grass species tested. Luminescence-based imaging of soil-grown root systems revealed a shift in root growth from crown to primary-root derived branches, suggesting that tap-root-like architecture can be induced in S. viridis under certain stress conditions. Crown roots of Zea mays (maize) and Setaria italica, domesticated relatives of teosinte and S. viridis, respectively, show reduced sensitivity to water deficit, suggesting that this response may have been influenced by human selection. Enhanced water status of maize mutants lacking crown roots suggests that, under water deficit, stronger suppression of crown roots may actually benefit crop productivity.