Os03g0633500

The rice gene Os03g0633500 was reported as OsIAA11 in 2012. It is a member of the rice Aux/IAA family genes.

Annotated Information

Function

• The mutation of OsIAA11 results in a defect in lateral root primordial initiation but does not affect crown root development.

• The auxin reporter DR5–GUS (b-glucuronidase) was expressed at lower levels in the mutant than in wild-type, indicating that OsIAA11 is involved in auxin signaling in root caps.

• The transcript abundance of both OsPIN1b and OsPIN10a was diminished in root tips of the Osiaa11 mutant.

Mutation

• One mutant that failed to develop lateral roots was isolated. The mutant showed longer and thicker roots, but no significant differences in the number of crown roots at seedling stages between the mutant and the wild-type (WT) plants (Figure 1A and 1B). The primary root length and root diameter of 7-day-old mutants increased about 10 and 20%, respectively, compared to WT (Figure 1). The mutant also showed a reduced response to gravity. A population derived from a cross between Osiaa11 mutant and its WT plants showed the segregation of WT, reduced lateral roots, and lateral rootless phenotypes at a ratio of 1:2:1, indicating that the defect in LR in the mutant is controlled by a single semi-dominant gene (Figure 1A). Osiaa11 mutant showed reduced plant height, tiller number, and panicle number, but had similar fertility compared to WT.

• To determine whether the initiation of lateral root primordia is impaired in the mutant, longitudinal sections of the root region where lateral roots emerged in WT plants were prepared. The microscopic investigation showed no LRP in the mutant (Figure 1C).

Figure 1. Morphology of Mutant Seedlings. (A) Phenotype of 7-day-old seedlings of wild-type (left), homozygous mutant (center), and heterozygous mutant (right). Bar = 2 cm. (B) Roots of 21-day-old plants of wild-type (left) and homozygous mutant (right). Bar = 4 cm. (C) Longitudinal sections of wild-type (n = 10) (left) and mutant (n = 20) (right) primary roots, 1–2.5 cm from the root tip. e, endodermis; p, pericycle; c, cortex. Bars = 25 lm. (D, E) Cross-sections of the wild-type (D) and the mutant (E) primary roots, 1–2.5 cm from the root tip, showing methylene blue staining (n = 10). Bars = 50 lm. .

• Auxin sensitivity in the Osiaa11 mutant was investigated. After treatments with NAA (naphthaleneacetic acid) at 0.1 lM for 7 d, the Osiaa11 mutant showed strong resistance to exogenousNAA compared toWT in a root elongation assay, yet lateral rootswerenot inducedinthemutant (Figure4A).Theexogenous auxin treatment induced the proliferation of root hairs toward the root tips of WT; however, no visible induction of root hairs was observed in the Osiaa11 mutant (Figure 4B and 4C). DR5:GUS is widely used for visualizing auxin response maxima. To investigate auxin signaling in the Osiaa11 mutant, the DR5:GUS construct was transformed into WT plants and Osiaa11 mutants. In WT roots, GUS staining was observed in the distal region of the root, root cap, and stele. In contrast, in the Osiaa11 mutant, GUS staining was observed in the stele and apical meristem but not in the root cap (Figure 4E and 4F). Cross-sections of the primary root at lateral root primordia emergence region showed that the GUS staining in the stele was similar between the Osiaa11 mutant and WT. In addition, the cell structure of the stele of Osiaa11 mutant was normal compared to WT (Figure 4G–4J).

Figure 4. Auxin Signaling Is Altered in the Osiaa11 Mutant. (A–C) Phenotype of 7-day-old seedlings of the wild-type (left) and the iaa11 mutant (right) grown in a solution culture with 10-7 M NAA. Proliferation of root hairs of WT (B) and Osiaa11 (C) induced by 10-7 M NAA treatment. (D, E) DR5:GUS expression in primary root tips of 7-day-old seedlings of WT and Osiaa11 mutant. (F) DR5:GUS expression in primary root stele of 7-day-old seedlings of WT and Osiaa11 mutant. (G, H) Cross-sections of the lateral root primordium in primary root of WTseedling. (H) is the magnification of (G). e, endodermis; p, pericycle. Bar = 50 lm. (I, J) Cross-sections of the lateral root primordium in primary root of Osiaa11 mutant seedling. (J) is the magnification of (I). e, endodermis; p, pericycle. Bar = 50 lm. .

• The results showed that transcript abundance of OsPIN1b and OsPIN10a was decreased in the root tips of Osiaa11mutant compared to that ofWT(Figure 5A). To confirm the results, transgenic plants harboring OsPIN1b:GUS and OsPIN10a: GUS were developed. GUS staining in root tips of the T2 plants in the Osiaa11 background were reduced compared with that of WT, which was consistent with our results from qRT–PCR analysis (Figure 5B–5E).

Figure 5. Expression of OsPIN1b and OsPIN10a Were Reduced in the Root Tip of Osiaa11 Mutant Compared with WT. .

Expression

• Quantitative reverse transcription PCR (RT–PCR) analysis showed that OsIAA11 is highly expressed in roots and stem-base (SB), but not in leaf, stem, and panicle (Figure 3A), which is consistent with previous reports (Jain et al., 2006; Song et al., 2009a). To further determine the expression patterns of OsIAA11, transgenic plants harboring GUS reporter driven by the promoter of OsIAA11 (OsIAA11p:GUS) were developed. GUS staining in roots showed that OsIAA11 was expressed in the root tip, lateral root cap, stele, lateral root primordia, and lateral root (Figure 3B–3G).

Figure 3. Tissue Expression Patterns of OsIAA11. (A) Quantitative RT–PCR analysis of expression of OsIAA11 in root and stembase (SB) of 7-day-old wild-type seedlings, and in stem, leaf, and panicle of matured plants. (B–G) Expression patterns of OsIAA11 indicated by GUS reporter gene driven by promoter of OsIAA11. Longitudinal view of a radicle root tip showing methylene blue staining. The arrow head indicates lateral root cap (lrc) and columella (co) (B). The GUS staining in the root tip (C), stele and lateral root primordia (LRP) (D), cross-section of lateral root primordium, the arrow indicates the LRP (E, F), and lateral root (G). Bar = 1 mm for (D), bar = 50 lm for (E). .

Labs working on this gene

• State Key Laboratory of Plant Physiology and Biochemistry, Zhejiang University, Hangzhou 310058, People’s Republic of China
• College of Life Sciences, Zi Jin Gang Campus, Zhejiang University, 866 Yu Hang Tang Road, Hangzhou, 310058, People’s Republic of China