Abstract
Root system architecture is very important for plant growth and crop yield. It is essential for nutrient and water uptake, anchoring, and mechanical support. Root growth angle (RGA) is a vital constituent of root system architecture and is used as a parameter for variety evaluation in plant breeding. However, little is known about the underlying molecular mechanisms that determine root growth angle in rice (Oryza sativa). In this study, a rice mutant large root angle1 (lra1) was isolated and shown to exhibit a large RGA and reduced sensitivity to gravity. Genome resequencing and complementation assays identified OsPIN2 as the gene responsible for the mutant phenotypes. OsPIN2 was mainly expressed in roots and the base of shoots, and showed polar localization in the plasma membrane of root epidermal and cortex cells. OsPIN2 was shown to play an important role in mediating root gravitropic responses in rice and was essential for plants to produce normal RGAs. Taken together, our findings suggest that OsPIN2 plays an important role in root gravitropic responses and determining the root system architecture in rice by affecting polar auxin transport in the root tip.
Highlights
Roots play a central role in plant growth and development through providing anchorage and taking up nutrients and water from the soil
The primary root length, shoot length, root number, lateral root number, longest lateral root length, and the total lateral root length were not significantly affected in the lra1 mutant compared with the WT after 7 d in solution culture (Supplementary Fig. S1), but lra1 showed larger root
There were no significant differences in shoot length, root length, and root number in 4-week-old seedlings grown in solution culture between lra1 and WT (Fig.1F–H)
Summary
Roots play a central role in plant growth and development through providing anchorage and taking up nutrients and water from the soil. Root growth angle (RGA) is an important parameter of root system architecture in the soil. Large RGAs (shallow root growth) are being deployed as targets in crop breeding programs for improving nutrient uptake efficiency in stressful soil environments (Lynch, 2013). Shootward auxin distribution in the lower side of the root is largely repressed during gravity stimulus, resulting in an agravitropic phenotype (Chen et al, 1998; Luschnig et al, 1998; Müller et al, 1998; Utsuno et al, 1998). Pin seedlings display decreased root gravitropic responses and inhibited hypocotyl and root growth (Friml et al, 2002; Harrison and Masson, 2008; Keuskamp et al, 2010). Genetic, and physiological analyses demonstrated that OsPIN2 plays an important role in rice root gravitropism and in determining the RGA via effects on the polar auxin transport in the root tip
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