Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2013 Oct 4;8(10):e75997.
doi: 10.1371/journal.pone.0075997. eCollection 2013.

Overexpression of OsEXPA8, a root-specific gene, improves rice growth and root system architecture by facilitating cell extension

Nana Ma  1 , Ying Wang, Shichun Qiu, Zhenhui Kang, Shugang Che, Guixue Wang, Junli Huang
Affiliations

Overexpression of OsEXPA8, a root-specific gene, improves rice growth and root system architecture by facilitating cell extension

Nana Ma et al. PLoS One. .

Abstract

Expansins are unique plant cell wall proteins that are involved in cell wall modifications underlying many plant developmental processes. In this work, we investigated the possible biological role of the root-specific α-expansin gene OsEXPA8 in rice growth and development by generating transgenic plants. Overexpression of OsEXPA8 in rice plants yielded pleiotropic phenotypes of improved root system architecture (longer primary roots, more lateral roots and root hairs), increased plant height, enhanced leaf number and enlarged leaf size. Further study indicated that the average cell length in both leaf and root vascular bundles was enhanced, and the cell growth in suspension cultures was increased, which revealed the cellular basis for OsEXPA8-mediated rice plant growth acceleration. Expansins are thought to be a key factor required for cell enlargement and wall loosening. Atomic force microscopy (AFM) technology revealed that average wall stiffness values for 35S::OsEXPA8 transgenic suspension-cultured cells decreased over six-fold compared to wild-type counterparts during different growth phases. Moreover, a prominent change in the wall polymer composition of suspension cells was observed, and Fourier-transform infrared (FTIR) spectra revealed a relative increase in the ratios of the polysaccharide/lignin content in cell wall compositions of OsEXPA8 overexpressors. These results support a role for expansins in cell expansion and plant growth.

PubMed Disclaimer

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Stiffness-properties imaging by atomic force microscopy (AFM) technology.
(A) Optical image of a typical single rice cell sample. The shadow of the AFM cantilever is visible on the left-hand side of the image. (B) A typical force-distance (FD) curve recorded on a single rice cell sample. The upper line represents the FD curve when the tip indents (or penetrates) the cell wall and the lower line represents the FD curve when the tip retracts from the cell wall.
Figure 2
Figure 2. mRNA level analyses for OsEXPA8 by quantitative real-time PCR in 35S::OsEXPA8 transgenic lines.
Mature leaves of eight independent adult transgenic lines harboring 35S::OsEXPA8 and wild-type (WT) rice plants were used for investigating OsEXPA8 expression. L1–L8 (line 1 to line 8) represents eight independent transgenic lines. Values are the means of three biological replications ± standard error. One independent transgenic plant was considered as one biological replication.
Figure 3
Figure 3. Morphological changes in 35S::OsEXPA8 transgenic lines.
(A) Seven-day-old rice seedlings of wild-type and 35S::OsEXPA8 transgenic line1 plants. (B, C) Stereoscope images of the primary root of wild-type (B) and 35S::OsEXPA8 line1 (C) seedlings. Scale bars = 40 µm. (D, E) Epidermal morphology of the root hair growth zones of seminal roots of wild-type (D) and 35S::OsEXPA8 line1 (E) seedlings. Scale bars = 10 µm. Seedlings were grown for 7 days on half-strength solid MS medium vertically, and the root apex of was observed by stereoscope microscopes and cryo-scanning electron microscope (Cryo-SEM), respectively. (F) Root system architecture of two-month-old wild-type and 35S::OsEXPA8 line1 plants. (G) The plant morphology of two-month-old wild-type and 35S::OsEXPA8 line1 plants. (H) Flag leaf phenotype of two-month-old wild-type and 35S::OsEXPA8 line1 plants.
Figure 4
Figure 4. Effect of overexpression of OsEXPA8 on the root system architecture and plant growth.
(A) The length of primary roots of seven-day-old rice seedlings. (B) The number of lateral roots of seven-day-old rice seedlings. (C) The plant height of two -month-old rice plants. (D) The leaf number per plant of two-month-old rice plants. (E) The length of the flag leaf of two-month-old rice plants. (F) The width of the flag leaf of two-month-old rice plants. Three independent transgenic line 1 (L1), line 4 (L4) and line 5 (L5) were analyzed. WT: wild-type. Values are the means of ten biological replications ± standard error. One independent plant was considered as one biological replication. Asterisks (*) indicate parameters of 35S::OsEXPA8 transgenic plants were significantly different from that of wild-type plants by statistical analysis using the Student’s t-test program (P<0.01).
Figure 5
Figure 5. Morphological changes of vascular bundle cells in both leaves and roots in rice 35S::OsEXPA8 transgenic line 1 plants
. Plants of two-month-old were subject to anatomic analysis. The cells were analyzed in an optical microscope. (A), (C), (E) and (G) wild-type plants; (B), (D), (F) and (H) 35S::OsEXPA8 transgenic lines; (A) and (B) transverse sections of the flag leaf, (C) and (D) longitudinal sections of the flag leaf; (E) and (F) transverse sections of the lateral root, (G) and (H) longitudinal sections of the lateral root. Scale bars: 25 µm.
Figure 6
Figure 6. Effect of OsEXPA8 overexpression on the cell length of vascular bundles in the flag leaf and lateral root.
(A) The cell length of flag leaf vascular bundles. (B) The cell length of lateral root vascular bundles. Three independent transgenic line 1 (L1), line 4 (L4) and line 5 (L5) were analyzed. WT: wild-type. n = 100 for metaxylem cells from ten plants. Values are the means of 10 biological replications ± standard error. Asterisks (*) indicate the cell parameters of 35S::OsEXPA8 transgenic lines were significantly different from that of wild-type cells (t-test, P<0.01).
Figure 7
Figure 7. The growth rate of 35S::OsEXPA8 suspension cells.
(A) pH value of growth medium, (B) The growth rate of suspension cells per day for 35S:OsEXPA8 transgenic line 1 (L1) and wild-type cultures monitored with the passage of time in culture. WT: wild-type. Values are the means of three biological replications ± standard error.
Figure 8
Figure 8. Cell wall stiffness profiles of wild-type and 35S::OsEXPA8 suspension cells with the passage of time in culture.
(A) and (B) on day 5, (C) and (D) on day 10, (E) and (F) on day 13. Each graph corresponds to stiffness values of 150 FD curves obtained on 30 cells, which derived from three biological replications from 35S::OsEXPA8 transgenic line 1. WT: wild-type.
Figure 9
Figure 9. Behavior of infrared absorption bands in cell wall isolates.
Cell wall isolates of wild-type and 35S::OsEXPA8 transgenic line 1 suspension cells on day 10 was used for wall composition analysis. Average and area-normalized Fourier-transform infrared (FTIR) spectra of isolated cell walls from wild-type (lower) and 35S::OsEXPA8 (upper) line 1 suspension cells.
See this image and copyright information in PMC

Similar articles

See all similar articles

Cited by

See all "Cited by" articles

References

    1. Zenoni S, Reale L, Tornielli GB, Lanfaloni L, Porceddu A, et al. (2004) Downregulation of the Petunia hybrida alpha-expansin gene PhEXP1 reduces the amount of crystalline cellulose in cell walls and leads to phenotypic changes in petal limbs. Plant Cell 16: 295–308. - PMC - PubMed
    1. Cosgrove DJ (2005) Growth of the plant cell wall. Nature Reviews Molecular Cell Biology 6: 850–861. - PubMed
    1. Cosgrove DJ (2000) Loosening of plant cell walls by expansins. Nature 407: 321–326. - PubMed
    1. McQueen-Mason SJ, Cosgrove DJ (1995) Expansin mode of action cell-walls-analysis of wall hydrolysis, stress-relaxation, and binding. Plant Physiology 107: 87–100. - PMC - PubMed
    1. Brummell DA, Harpster MH, Civello PM, Palys JM, Bennett AB, et al. (1999) Modification of expansin protein abundance in tomato fruit alters softening and cell wall polymer metabolism during ripening. Plant Cell 11: 2203–2216. - PMC - PubMed

MeSH terms

Grants and funding

This work was supported by the National Natural Science Foundation of China (grant no.31271685) and Fundamental Research Funds for the Central Universities (grant no. CQDXWL-2012-114). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.