Isolation And Functional Analysis Of Leaf Senescence-related Genes In Bamboo

Leaf senescence is an organ level senescence and constitutes the final stage of leaf development. Although leaf senescence is a deleterious process for the sake of the leaf organ, it is critical for the achievement of plants'fitness as nutrient relocation from leaves to other developing organs. Leaf senescence is thus an evolutionarily selected developmental process and comprises an important phase in the plant life.Yellowing of leaves is the most easily observed appearance during leaf senescence.AtNYEl is an important chlorophyll degradation regulatory gene. And nyel-1 mutant showed significant stay-green phenotype. We isolated a leaf senescence-related gene from Bambusa emeiensis'Viridiflavus'by RACE-PCR. The full-length cDNA of this gene was 1386bp, encoding a putative protein of 266 amino acids. Sequence analysis indicated that it's protein sequence shared approximately 66% similarity with AtNYEl and was the most similar with SGR from Oryza sativa, so tentatively named BeNYEl. BeNYE1 was induced by natural senescence and dark-induced senescence in bamboo. The functional complementation of BeNYE1 demonstrated that BeNYE1 could rescue the stay-green phenotype of Arabidopsis nyel-1 mutant, and both the transient overexpression and constitutive overexpression of BeNYEl accelerate chlorophyll degradation, resulting in the yellowing of leaves. All the results demonstrated that BeNYEl encodes an AtNYEl like regulator of chlorophyll degradation, and play an important role in the process of chlorophyll degradation in bamboo.NAC (NAM, ATAF 1,2 and CUC2) proteins are plant-specific transcription factors, and have crucial roles in plant development, organ formation, hormonal regulation, biotic and abiotic stress responses, defense, etc. In this study, we isolated a NAC transcription factor from the cDNA library of bamboo's senescence leaf by RACE-PCR. This transcription factor had a total length of 1654bp, encoding a predicted polypeptide of 355 amino acids. The N-terminal region of it's protein had a highly conserved NAC domain, so tentatively named BeNACl. BeNACl located in nucleus and had transcriptional activation activity as with other transcription factors. Sequence analysis indicated that BeNACl belonged to NAP subfamily and shared a high similarity with OsNAP from Oryza sativa. AtNAP involved in the regulaion of leaf senescence as a NAC transcription factor in Arobidopsis. The functional analysis showed that, BeNACl was strongly induced by natural senescence and dark-induced senescence in bamboo with a similar express pattern of AtNAP, and BeNACl could rescue the delayed-senescence phenotype of Arabidopsis nap null mutant. In addition, the overexpression of BeNACl caused precocious senescence of transgenic lines, which further indicated that BeNAC1 was a functional homolog of AtNAP, and play an important role in the regulation of leaf senescence in Bambusa emeiensis'Viridiflavus'.Bamboo is featured by rapid growth, high biomass and diversified applications. It displayed a huge advantage and potential in the fields of architecture, papermaking, ornament for environment, health-care food, landscaping and ecological protection, etc. In this study, we tried to explore the function of leaf senescence-related gene in bamboo through the research system of model plant Arabidopsis, and provided valid genetic resources for the improvement of bamboo's horticultural traits.