| The plasticity of plant architecture is dependent on the plant's ability to respond to environmental cues. Vectorial cues such as gravity, light, oxygen, water, nutrients, and mechanical force guide the directional growth of plant organs, producing growth behaviors adaptive to specific environments. Few genes have been implicated in rapid plant responses to their mechanical environment. We conducted a proteomic screen to identify tris-buffer soluble root-tip proteins whose abundance varies early in the response to reorientation within the gravity field. SEC62-LIKE1 (SSL1), encoded by locus AT3G20920, is described here for the first time in plants. The staining intensity of spots on 2-D PAGE gels representing SSL1 increased within 12 minutes of the gravity or mechanical stimulus. Several independent mutant alleles of SSL1 are shown to display aberrant root-growth behavior on tilted hard-agar surfaces, suggesting a role for this gene in modulating this gravity- and touch-dependent process. One of the insertional mutants, named ssl1-2 FLAG, was further characterized. This loss-of-function mutation inhibits root skewing on hard-agar surfaces without affecting root gravitropism. The mutant also shows altered root growth in response to various mechanical stresses as compared to the wild type, and it displays adult phenotypes consistent with constitutive thigmomorphogenesis. It also shows increased sensitivity to a microtubule-destabilizing drug compared to the wild type. A SSL1 transgene rescues the adult phenotypes associated with ssl1-2FLAG. Taken together, our data are consistent with SSL1 functioning early in mechano-transduction, with possible effects on the organization and/or dynamic instability of cortical microtubules in expanding cells of the elongation zone. |
