Abstract
Root angle has a major impact on acquisition of nutrients like phosphate that accumulate in topsoil and in many species; low phosphate induces shallower root growth as an adaptive response. Identifying genes and mechanisms controlling root angle is therefore of paramount importance to plant breeding. Here we show that the actin-binding protein Rice Morphology Determinant (RMD) controls root growth angle by linking actin filaments and gravity-sensing organelles termed statoliths. RMD is upregulated in response to low external phosphate and mutants lacking of RMD have steeper crown root growth angles that are unresponsive to phosphate levels. RMD protein localizes to the surface of statoliths, and rmd mutants exhibit faster gravitropic response owing to more rapid statoliths movement. We conclude that adaptive changes to root angle in response to external phosphate availability are RMD dependent, providing a potential target for breeders.
Highlights
Root angle has a major impact on acquisition of nutrients like phosphate that accumulate in topsoil and in many species; low phosphate induces shallower root growth as an adaptive response
The Rice Morphology Determinant (RMD) gene is expressed in rice root columella cells (Fig. 1a) and rmd mutants exhibit altered shoot and wavy root growth behaviours[20], prompting us to test whether this gene regulates root gravitropism
To understand whether RMD is required for phosphate-dependent changes in root angle, we investigated the impact of disrupting RMD function under high phosphate (HP) and low phosphate (LP) conditions
Summary
Root angle has a major impact on acquisition of nutrients like phosphate that accumulate in topsoil and in many species; low phosphate induces shallower root growth as an adaptive response. Recent work in Arabidopsis has shown that lateral roots with non-vertical GSAs are distinguished from the primary roots with ~vertical GSAs by the action of an auxin-dependent offset mechanism that counterbalances underlying gravitropic response in the root branch[11,13]. In this system, root growth angles are the product of the relative magnitude of the gravitropic and the counterbalancing offset components, with variation in either providing a means to alter GSA10,11,13. We propose that RMD acts to fine-tune root angle in response to soil phosphorus availability
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