Plants adapt to heterogeneous soil conditions by altering their root architecture. For example, roots branch when in contact with water by using the hydropatterning response. We report that hydropatterning is dependent on auxin response factor ARF7. This transcription factor induces asymmetric expression of its target gene LBD16 in lateral root founder cells. This differential expression pattern is regulated by posttranslational modification of ARF7 with the small ubiquitin-like modifier (SUMO) protein. SUMOylation negatively regulates ARF7 DNA binding activity. ARF7 SUMOylation is required to recruit the Aux/IAA (indole-3-acetic acid) repressor protein IAA3. Blocking ARF7 SUMOylation disrupts IAA3 recruitment and hydropatterning. We conclude that SUMO-dependent regulation of auxin response controls root branching pattern in response to water availability.

Plants are sessile organisms rooted in one place. The soil resources that plants require are often distributed in a highly heterogeneous pattern. To aid foraging, plants have evolved roots whose growth and development are highly responsive to soil signals. As a result, 3D root architecture is shaped by myriad environmental signals to ensure resource capture is optimised and unfavourable environments are avoided. The first signals sensed by newly germinating seeds - gravity and light - direct root growth into the soil to aid seedling establishment. Heterogeneous soil resources, such as water, nitrogen and phosphate, also act as signals that shape 3D root growth to optimise uptake. Root architecture is also modified through biotic interactions that include soil fungi and neighbouring plants. This developmental plasticity results in a 'custom-made' 3D root system that is best adapted to forage for resources in each soil environment that a plant colonises.

Highlights d Cereal plants repress lateral root formation in soil air spaces d ABA treatment can mimic this xerobranching response d Transient ABA application decreases auxin above the root apical meristem d ABA irreversibly prevents acquisition of lateral root founder cell identity

Plant roots exhibit plasticity in their branching patterns to forage efficiently for heterogeneously distributed resources, such as soil water. The xerobranching response represses lateral root formation when roots lose contact with water. Here, we show that xerobranching is regulated by radial movement of the phloem-derived hormone abscisic acid, which disrupts intercellular communication between inner and outer cell layers through plasmodesmata. Closure of these intercellular pores disrupts the inward movement of the hormone signal auxin, blocking lateral root branching. Once root tips regain contact with moisture, the abscisic acid response rapidly attenuates. Our study reveals how roots adapt their branching pattern to heterogeneous soil water conditions by linking changes in hydraulic flux with dynamic hormone redistribution.

Vertebrate color vision relies on the differential expression of visual pigment proteins (opsins) in cone photoreceptors of the retina. The diversity of opsins and their retinal expression patterns appear greatest for animals that experience variable light habitats, as is the case with flatfishes. Yet, opsin repertoires and expression patterns in this group of fishes are poorly described. Here, we unveil the visual opsin expression patterns of juvenile starry flounder (Platichthys stellatus) and describe the localization of cone types, their visual pigments and opsin expression. Juvenile starry flounder express eight opsins (Rh1, Sws1, Sws2A1, Sws2A2, Sws2B, Rh2A1, Rh2A2, Lws) and possess a corresponding number of photoreceptor visual pigments, with peak absorbance ranging from 369 to 557 nm. Retinal (vitamin A1) was the only chromophore detected in the retina. Intraretinal variation in opsin abundance consisted of greater expression of both RH2, and lesser expression of SWS1 and both SWS2A, opsin transcripts in the dorsal compared to the ventral retina. Overall cone density was greater in the dorsal retina which was also characterized by a larger proportion of unequal double cones compared with the ventral retina. Together, our results suggest that large opsin repertoires serve to optimize visual function under variable light environments by differential expression of opsin subsets with retinal location.