Date Published: July 14, 2017
Publisher: Public Library of Science
Author(s): Yongxing Zhang, Chunsheng Yu, Jianzhong Lin, Jun Liu, Bin Liu, Jian Wang, Aobo Huang, Hongyu Li, Tao Zhao, Jin-Song Zhang.
Plant height is a major trait affecting yield potential in rice. Using a large-scale hybrid transcription factor approach, we identified the novel MYB-like transcription factor OsMPH1 (MYB-like gene of Plant Height 1), which is involved in the regulation of plant height in rice. Overexpression of OsMPH1 leads to increases of plant height and grain yield in rice, while knockdown of OsMPH1 leads to the opposite phenotypes. Microscopy of longitudinal stem sections indicated that a change in internode cell length resulted in the change in plant height. RNA sequencing (RNA-seq) analysis of transgenic rice lines showed that multiple genes related to cell elongation and cell wall synthesis, which are associated with plant height and yield phenotypes, exhibited an altered expression profile. These results imply that OsMPH1 might be involved in specific recognition and signal transduction processes related to plant height and yield formation, providing further insights into the mechanisms underlying the regulation of plant height and providing a candidate gene for the efficient improvement of rice yield.
Plant height is an important agronomic trait of rice that directly affects the yield of this crop. The dwarf phenotype is beneficial for rice lodging, but if the plants are too short, it will lead to insufficient growth and ultimately affect the yield potential of rice. Therefore, in an absence of lodging, it is essential to increase plant height to increase yield. The second green revolution and the breeding of super rice are based on appropriate plant heights [1–3]. Therefore, it is of great significance to explore and identify plant height genes and apply them to rice breeding.
Plant height is closely related to biomass production, which makes it an important morphological trait that affects yield performance. Rice is an economically important crop, in which the ratio of economic output to biological yield is 1:1. Therefore plant height and yield are closely related, and within a certain range, when plant height is increased, the yield is also increased. A moderate plant height is an important basis for rice breeding. In the present study, we identified a new rice MYB gene, OsMPH1, which might function in plant height regulation. OsMPH1 is highly expressed in the rice pulvinus and nodes, and the encoded protein is exclusively localized in the nucleus. OsMPH1 overexpression leads to an increase of plant height, caused by longitudinal elongation of internode cells. Our result also indicated that OsMPH1Es plants shared the similar phenotype with OsMPH1 overexpression plants, while OsMPH1V and OsMPH1-RNAi plants exhibited the opposite phenotype. Combining with the transcription activation analysis result that OsMPH1V functions as a transcriptional activator and OsMPH1E functions as a suppressor, OsMPH1 might work as a transcriptional suppressor in vivo. Considering that OsMPH1 bears almost no transcriptional activity, recruitment of a partner may be necessary for OsMPH1 to implement the activator function of the plant height.Plant cell elongation growth is regulated by a variety of internal and external factors, and the regulation of endogenous hormones in plants plays an important role in this process. For example, auxin (IAA), gibberellin (GA), brassinolide (BR) and ethylene (ETH) can regulate cell elongation, and the interaction between the sources of hormones directly or indirectly regulates cell elongation. It has been reported that AtMYB52, AtMYB54, and AtMYB69 regulate the biosynthesis of lignin, xylan, and cellulose, participating in secondary cell wall thickening (Stracke et al. 2001; Zhong et al. 2008). OsMPH1 may exhibit functions similar to these transcription factors, particularly in cell wall development. In plants, hormones including small organic molecules as well as larger peptides and small proteins act as ligands and interact with receptor proteins to trigger rapid biochemical changes and induce intracellular transcriptional and long-term physiological responses. Receptor kinases have been demonstrated to be important for cell elongation. For example, auxins can stimulate cell elongation by activating ROPs [Rho-like guanosine triphosphatases (GTPase)], and the TMK receptors-like kinases activate ROP activators, such as ROP-GEF, via phosphorylation to activate ROPs [22, 23]. The cell wall-associated receptor kinase WAK4 has been reported to be involved in cell elongation and plant development. WAK4 antisense expression results in cell elongation and developmental arrest . Our further investigation showed that WAK4 homologous genes in rice, including LOC_Os02g42150, LOC_Os04g30010, LOC_Os09g29560 and LOC_Os04g51030, were up-regulated in OsMPH1V transgenic plants but down-regulated in OsMPH1E transgenic plants. A previous study identified 27 AtWAKs in Arabidopsis and 130 OsWAKs in rice, suggesting functional diversification in Arabidopsis and rice [24, 25]. Therefore, these four genes might be involved in the regulation of cell elongation, differing from the functions observed in Arabidopsis. Additional efforts focusing on the functional activity of these genes will be helpful to understand the regulation of cell elongation in rice. Furthermore, we identified a series of indole biosynthetic pathway genes whose expression patterns were changed in the transgenic plants, which implied that auxin-regulated cell elongation is an important component of the variation in plant height.