Since the identification of the DRO1 gene in rice in 2011, which regulates root gravitropism, research on the genetic control of root angle has expanded to wheat. Unlike rice, which has a major gene like DRO1, wheat lacks such a single dominant gene. Instead, its root angle is a complex trait controlled by multiple genes. Studies have demonstrated that the seminal root angle in seedlings can be associated with root distribution at later growth stages, particularly in shallow soil layers. However, this relationship varies depending on the methods used to assess root growth angles and the specific field conditions. Among the various evaluation techniques, the basket and clear pot methods using soil have proven more effective for predicting root system architecture in the field. Wheat lines with contrasting root depths have been developed. The link between root angle and yield remains inconclusive. One study reported that shallow-rooted lines yielded 15% more under waterlogged conditions, although this difference was not statistically significant. Additionally, under long-term no-till management, shallow-rooted lines have shown significantly higher yields in some cases. Roots exhibit high plasticity and adapt to their soil environment. Future research should focus on identifying optimal root system architectures for specific environments and developing wheat cultivars with ideal root traits by pyramiding multiple genetic loci.

Rice produces two distinct types of lateral roots, S-type and L-type, which differ in morphology, anatomy, and function. Hardpans in rainfed lowlands or compacted soils restrict deep rooting and reduce crop productivity, whereas plastic development of lateral roots helps maintain shoot growth when the rooting zone is limited. However, the genetic basis of such root plasticity has remained unclear due to the difficulty of observing underground traits. Here, we investigated the regulatory mechanisms controlling plastic lateral root formation in rice using a seminal-root tip excision method. Mutant analysis revealed that the WUSCHEL-RELATED HOMEOBOX (WOX) family transcription factor QHB/OsWOX5 acts as a brake that limits the size of lateral root primordia. Transcriptome comparison between S-type and L-type primordia further identified OsWOX10 as an accelerator that promotes primordium enlargement. The expression of OsWOX10 is directly repressed by QHB/OsWOX5. We also found that auxin distribution contributes to primordium size control: in L-type primordia, auxin accumulates at the basal region, leading to OsWOX10 activation. Using a semi-hydroponic phenotyping system, we demonstrated that L-type lateral roots induced after root-tip excision compensate for the loss of further main root elongation and help maintain overall root system development and shoot growth. These findings reveal the molecular framework underlying plastic lateral root development in rice and highlight its importance for plant growth under restricted rooting-zone conditions.