An R2R3-MYB Transcription Factor OsMYBAS1 Promotes Seed Germination under Different Sowing Depths in Transgenic Rice

Abstract

MYB-type transcription factors play essential regulatory roles in seed germination and the response to seedling establishment stress. This study isolated a rice R2R3-MYB gene, OsMYBAS1, and functionally characterized its role in seed germination by generating transgenic rice plants with the overexpression and knockout of OsMYBAS1. Gene expression analysis suggested that OsMYBAS1 was highly expressed in brown rice and root, respectively. Subcellular localization analysis determined that OsMYBAS1 was localized in the nucleus. No significant differences in seed germination rate were observed among wild-type (WT) and transgenic rice plants at the 0-cm sowing depth. However, when sown at a depth of 4 cm, higher germination rates, root lengths and seedling heights were obtained in OsMYBAS1-overexpressing plants than in WT. Furthermore, the opposite results were recorded between the osmybas1 mutants and WT. Moreover, OsMYBAS1-overexpressing plants significantly enhanced superoxide dismutase (SOD) enzyme activity and suppressed the accumulation of malondialdehyde (MDA) content at the 4-cm sowing depth. These results indicate that the MYB transcription factor OsMYBAS1 may promote rice seed germination and subsequent seedling establishment under deep-sowing conditions. These findings can provide valuable insight into rice seed-quality breeding to facilitate the development of a dry, direct-seeding production system.

Keywords: MYB transcription factor; OsMYBAS1; antioxidant enzyme; deep-sowing; seed germination.

Figure 1

qRT-PCR analysis of the expression of OsMYBAS1 in different rice tissues. Data are mean ± SE of three biological replications. Asterisks indicate statistically significant differences (p < 0.05, Duncan test) from the control (glume). Actin was used as an internal control.

Figure 2

Subcellular localization analysis of OsMYBAS1. Confocal images of rice protoplasts cells under the GFP channel showing the constitutive localization of GFP and the nuclear localization of OsMYBAS1-GFP. Confocal images of rice protoplasts cells under the mCherry channel showing the constitutive localization of mCherry. The merged images of GFP and OsMYBAS1-GFP are presented, respectively.

Figure 3

Identification and phenotype of OsMYBAS1-overexpressing plants and osmybas1 mutants. (A) Relative expression of wild-type (WT) and two OsMYBAS1-overexpressing rice lines (OE-1 and OE-2); (B) leaf phenotype of WT and osmybas1 mutants (osmybas1-1 and osmybas1-2) soaked in Hygromycin solution; (C) two osmybas1 mutants (osmybas1-1 and osmybas1-2) were obtained by sequencing and the knockout sites are presented; (D) phenotype of WT, OsMYBAS1-overexpressing plants and osmybas1 mutants at the sowing depths of 0 and 4 cm, respectively. Data are mean ± SE of three biological replications. Asterisks indicate statistically significant differences (p < 0.05, Duncan test) from the control (glume). Actin was used as an internal control.