OsNAC2 Is Involved in Multiple Hormonal Pathways to Mediate Germination of Rice Seeds and Establishment of Seedling.

Chanjuan Mao,Jiangtao Yu,Qun Zhong,Xuefeng Yao,Chunming Liu,Peng Li,Feng Ming

doi:10.3389/fpls.2021.699303

Abstract

The germination of seeds and establishment of seedling are the preconditions of plant growth and are antagonistically regulated by multiple phytohormones, e.g., ethylene, abscisic acid (ABA), and gibberellic acid (GA). However, the interactions between these phytohormones and their upstream transcriptional regulation during the seed and seedling growth in rice remain poorly understood. Here, we demonstrated a rice NAC (NAM-ATAF-CUC) transcription factor, OsNAC2, the overexpression of which increases the ethylene sensitivity in rice roots during the seedling period. Further study proved that OsNAC2 directly activates the expressions of OsACO and OsACO3, enhancing ethylene synthesis, and then retards seedling establishment. Moreover, OsNAC2 delays the germination of seeds and coleoptile growth through the ABA pathway instead of the ethylene and GA pathway, by targeting the promoters of OsNCED3, OsZEP1, and OsABA8ox1. We also found that OsNAC2 regulates downstream targets in a time-dependent manner by binding to the promoter of OsKO2 in the seedling period but not in the germination stage. Our finding enriched the regulatory network of ethylene, ABA, and GA in the germination of rice seeds and seedling growth, and uncovered new insights into the difference of transcription factors in targeting their downstream components.

Highlights

Rice (Oryza sativa L.) is one of the most important cereal foods worldwide
Under the treatment with ACC, the inhibition rate of root and the promotion rate of sprout were significantly higher in the overexpression lines, which strongly suggested that OsNAC2 enhanced the ethylene sensitivity in both rice root and sprout (Figure 1A)
The ethylene contents of the OsNAC2RNAi lines were 401.7 and 311.0 nl/g.h, respectively, which were significantly lower than that of wild type (WT) (695.94 nl/g.h), while the OsNAC2-overexpressing line ON11 showed the highest ethylene emission (873.22 nl/g.h) (Figure 1C). These results indicated that OsNAC2 may affect the formation of rice seedlings by strengthening the ethylene response and synthesis

Summary

Introduction

Rice (Oryza sativa L.) is one of the most important cereal foods worldwide. During its life cycle, the germination of seeds and seedling formation are always the preconditions of plant growth and development. Besides ABA and GA, ethylene is generally recognized to promote the germination of seeds and acts as an antagonist to ABA in seeds of Arabidopsis and other species (Ghassemian et al, 2000; Kucera et al, 2005; Linkies et al, 2009; Matilla and MatillaVazquez, 2008). The constitutive ethylene-response mutant ctr showed a weakened ABA response in the germination of seeds (Beaudoin et al, 2000). It remains largely unknown how cross talk among ABA, GA, and ethylene modulates the germination of seeds, and their upstream components still need to be investigated

Methods

Results

Conclusion