Abstract
Lateral roots of Arabidopsis temporary grow obliquely relative to the gravity vector after the initiation and then grow downward. We study mechanism controlling growth direction of lateral roots by analyzing those of mutant hy5. In hy5 lateral roots, transition from oblique to downward growth is retarded. We built a mathematical model by expressing bending rate as a linear combination of sine and cosine of deviation of growth direction from gravity vector. The model fitted well to the plagiogravitropic root reorientation, implying that a mechanism sensing the two components of gravity separately contributes to the plagiogravitropism. We further estimated gravitropic set-point angle (GSA) based on the model and found that GSA declined with root elongation, and that the decline was retarded in hy5. Lateral roots of hy5 and wild-type grew more downward when antiauxin BH-IAA was applied. Because BH-IAA inhibits degradation of Aux/IAA, Aux/IAA accumulation may function in earlier transition to downward growth. We also screened for revertants of hy5 with earlier transition from oblique to downward growth in lateral roots. We found FtsH11 as a candidate for such suppressor genes.
