Cloning And Functional Analysis Of Development-related Genes TaMOR And TaPARG From Wheat(Triticum Aestivum L.)

Wheat(Triticum aestivum L.) is a staple food crop worldwide, but abiotic stress factors, such as drought and heat, seriously restrict the wheat production. To meet the urgent demand for food security, the wheat breeders are trying their best to breed better adapted cultivars for the fluctuating environments and having higher yield and as well as resistance against abiotic stresses. The root systems and plant architecture can directly affect the grain yield of wheat. Therefore revealing genetic mechanism of root system and ideal plant architecture development, discovering gene resources and favorable alleles are important approaches in wheat improvement. Gene families of AS2/LOB(ASYMMETRIC LEAVES2/LATERAL ORGAN BOUNDARIES) and AP2/EREBP(APETALA2/ETHYLENE-RESPONSIVE ELEMENT BINDING PROTEINS) transcription factor have significant role in plant growth and development. We cloned a Ta MOR(MORE ROOT) and Ta PARG(PLANT ARCHITECTURE-RELATED GENE) from a wheat cultivar Hanxuan 10, which belong to LOB and AP2/EREBP gene families, respectively. On the basis of gene sequence characteristics and gene functional analysis, Ta MOR and Ta PARG have been found to play an integral role in root or plant architecture development. The results are mainly exhibited as follows.1. Overexpression of Ta MOR gene from wheat results in increased number of roots and higher grain yield in rice. Ta MOR belongs to the AS2/LOB gene family, which is highly conserved in wheat and its relatives, the sequence similarities of Ta MOR-A, Ta MOR-B and Ta MOR-D amino acids and c DNAs are as high as 97.12% and 96.90%, respectively. Expression patterns indicated that Ta MOR mainly localizes to root initiation sites and Ta MOR expression patterns during germination and seedling development is consistent with the time of root initiation. The consistent gene expression pattern suggests that Ta MOR is involved in root initiation. Exogenous auxin treatment induced Ta MOR expression without de novo protein biosynthesis. Both in vivo and in vitro experiments demonstrated that Ta MOR interacts with Ta MRRP(Ta MOR-RELATED PROTEIN). Overexpression of Ta MOR leads to more lateral roots in Arabidopsis, and Ta MOR-overexpressing rice plants have more crown roots, longer main panicle, more primary branch number on the main panicle, more grain number per plant and higher yield per plant than the plants of wild type. In general, Ta MOR-D-overexpressing lines have larger root systems in Arabidopsis and rice accompanied with higher grain yield.2. A novel, pleiotropic Ta PARG, a member of the AP2/EREBP transcription factor gene family, play significant roles in regulating plant architecture-related and yield-related traits. Two Ta PARG alleles were identified and named as Ta PARG-2A and Ta PARG-2D. Amino acid sequences of these two genes were highly similar i.e. 97.67%, and the functional domains are completely consistent. Ta PARG-2A on chromosome 2A was flanked by markers Xwmc63 and Xgwm372. Ta PARG-2D was mapped to chromosome 2D. Subcellular localization revealed that Ta PARG-2D was localized in the nucleus. The results of tissue expression pattern, association analysis and overexpression in rice jointly revealed that Ta PARG functions during the entire growth cycle of wheat. Regulation of plant architecture(plant height and tiller number) and yield related trait(thousand kernel weight) are mainly governed by this gene. Three haplotypes are identified in Ta PARG-2A, and Hap-2A-2 and Hap-2A-3 are favored haplotypes which show better agronomic traits, including lower plant height, less tiller number and higher thousand kernel weight. Both favored haplotypes might be because of a single amino acid substitution(His/Tyr). Favored haplotypes Hap-2A-2 and Hap-2A-3 were positive selected in Chinese wheat breeding programs. These results suggest that Ta PARG is a regulatory factor in wheat growth and development, and that the favored alleles might be useful for improving plant architecture and grain yield of wheat.This study indicated the possibility of using Ta MOR and Ta PARG as promising tools for the development of better wheat root system, ideal plant architecture and ultimately a better wheat cultivar.