Abstract:

Melilotus is an important forage and green manure legume crop in northern China. It plays an important role in grass husbandry and ecological and economic construction in this region， and in greater China. Drought stress is an important factor affecting the distribution and yield of Melilotus. It is important to screen and characterize genes that regulate the response of Melilotus to drought stress to understand the drought resistance biology of this genus. The TCP （teosinte branches1， cycloidea， proliferating cell factory） family of transcription factors is specific to plants， and its members are known to play important roles in regulating the response to drought stress. The aim of this study was to identify members of this gene family in Melilotus and explore their biological functions in response to drought stress. In this study， the TCP gene family in Melilotusallbus was systematically identified at the whole-genome level using bioinformatics methods. Further analyses revealed details of TCP gene structures， phylogeny， chromosome locations， and expression patterns under drought stress. The genome of M. albus contained 18 MaTCP genes， which were unevenly distributed on six chromosomes. In a phylogenetic analysis， the 18 MaTCP genes were grouped into two subfamilies： TCP-P and TCP-C. The TCP-P subfamily contained only PCF branches， while the TCP-C subfamily contained CYC/TB1 and CIN branches. All of the 18 MaTCP genes contained a highly conserved bHLH domain and had similar conserved motifs and gene structures within the same subfamily， but members of the TCP-P family had four fewer amino acids in their bHLH domain. Analyses of the transcriptome data obtained for M. albus under drought stress revealed two MaTCP genes （MaTCP2 and MaTCP15） that may be related to the drought stress response. Quantitative reverse-transcription polymerase chain reaction analyses confirmed that， under drought stress simulated by a polyethylene glycol treatment， the transcript levels of MaTCP2 increased significantly in the root of M. albus， while the transcript levels of both genes in the leaf peaked at 3 h of the simulated drought treatment. These results confirmed that both genes are involved in the drought response in M. albus. The results of this study lay the foundation for further research on the drought response of Melilotus， and will be useful for generating Melilotus varieties with enhanced drought resistance through genetic engineering.

Key words: Melilotus albus, TCP gene, genome-wide identification, drought stress, expression profiles