Haiping Cheng

• Publications
• Research
• Slide Show

Publications

Xue-Song Zhang and Hai-Ping Cheng. 2006. Identification of Sinorhizobium meliloti early symbiotic genes by use of a positive functional screen. Applied Environmental Microbiology. 72: 2738-2748. [PDF]

Feng Chi, Shi-Hua Shen, Hai-Ping Cheng, Yu-Xiang Jing and Frank B. Dazzo. 2005. Ascending migration of endophytic rhizobia from roots to leaves inside rice plants. Applied Environmental Microbiology, 71:7271-7278. [PDF].

Li Luo, Shi-Yi Yao, Anke Becker, Silvia Ruberg, Guan-Qiao Yu, Jia-Bi Zhu, and Hai-Ping Cheng. 2005. Identification of two new Sinorhizobium meliloti lysR like transcriptional regulators required for nodulation. J. Bacteriology, 187: 4562-4572. [PDF].

Li Luo, Ming-Sheng Qi, Shi-Yi Yao, Hai-Ping Cheng, Jia-Bi Zhu, Shan-Jiong Shen, and Guan-Qiao Yu. 2005. Characterization of OxyR homolog from Sinorhizobium meliloti Rm1021 regulating the expression of catalase genes. Acta Biochimica et Biophysica Sinica, 37: 421-428. [PDF].

Shi-Yi Yao, Li Luo, Katherine Har, Anke Becker, Silvia Ruberg, Guan-Qiao Yu, Jia-Bi Zhu, and Hai-Ping Cheng. 2004. The Sinorhizobium meliloti ExoR and ExoS proteins regulate both succinoglycan and flagella production. J. Bacteriology, 186:6042-6049. [PDF].

Hai-Ping Cheng and Shi-Yi Yao. 2004 (Dec. 2003, online). The promoters of the Sinorhizobium meliloti exoY gene and their expression during nodulation. FEMS. Microbiology Letters, 231:131-136. [PDF].

Brett Pellock, Hai-Ping Cheng, and Graham C. Walker. 2000. Alfalfa root nodule invasion efficiency is dependent on Sinorhizobium meliloti. J. Bacteriology, 182:4310-4318. [PDF].

Hai-Ping Cheng and Graham C. Walker. 1998. Succinoglycan production of Rhizobium meliloti 1021 is regulated by the ExoS/ChvI two-component regulatory system. J. Bacteriology. 180: 20-26. [PDF].

Hai-Ping Cheng and Graham C. Walker. 1998. Succinoglycan is required for the formation of infection threads during the nodulation of alfalfa by Rhizobium meliloti 1021. J. Bacteriology. 180: 5183-5191. [PDF].

Anke Becker, S. Ruber, H. Kuster, A.A. Roxlau, M. Keller, T. Ivashina, Hai-Ping Cheng, G.C. Walker, and A. Pulher. 1997. The 32-Kilobase exp gene cluster of Rhizobium meliloti directing the biosynthesis of galactoglucan: genetic organization and properties of the encoded gene products. J. Bacteriology. 179:1375-1384. [PDF].

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Research

One of the most interesting microbe-plant interactions is the symbiosis between nitrogen fixing bacteria rhizobia and leguminous plants. The growth of a healthy plant depends on a lot of different factors, the availability of fixed nitrogen source such as ammonia is one. Most plants, except for the legume group, depend on the presence of a fixed nitrogen such as ammonia for their growth so that most of the plants are limited to grow in nutrient rich environments. Leguminous plants have developed a unique approach to solve this dependence on fixed nitrogen by forming a symbiosis with nitrogen fixing bacteria. Leguminous plants develop root nodules in the presence of rhizobia and those nodules are then colonized by rhizobia. The carbon and other nutrients provided by the plant support the growth of bacterial cells whose primary activity is to convert atmosphere nitrogen into ammonia as nitrogen source for the plant growth. The agriculture and environmental significance of this symbiosis has made the Sinorhizobia meliloti-alfalfa interaction one of the best understood model systems for microbe-plant interaction.

The successful establishment of the symbiosis appears to depend on intricate exchanges of chemical signal between S. meliloti cells and alfalfa, their plant host. Such signal exchanges would likely be the basis for the strict symbiotic relationship between S. meliloti and alfalfa, and the ability of alfalfa to prevent pathogenic bacteria in soil from colonizing its root nodules. It is currently understood that the start of this symbiosis is trigged by the exchange of the bacterial Nod factor and plant flavonoids. Like all other leguminous plants, alfalfa produces flavonoids and secrets into soils sounding their roots. The flavonoids elicit the production of the Nod factor by S. meliloti cells in the soil surrounding the roots. When the S. meliloti nod factor is sensed, alfalfa will form curled root hairs and infection thread inside these curled root hairs that will allow the bacterial cells to enter and colonize root nodules. One crucial question is how does alfalfa know when and where to form infection threads and selectively allow only its symbiotic rhizobial cells to enter the infection threads?

The introduction of the fluorescence labeling technology allowed us to focus on the process of the infection thread formation and bacterial entry to the infection threads. We discovered that the formation of infection thread depends on the presence of a bacterial polysaccharide, succinoglycan. We have introduced a jellyfish gene into rhizobial cells so that S. meliloti cells are constitutively producing green fluorescence protein that turns transparent bacterial cells into green under UV light. The green fluorescence protein does not interfere with the ability of the rhizobial cells to symbiosis with its plant host. By comparing symbiosis of rhizobial mutants that fail to produce a bacterial polysaccharide, succinoglycan, to those of their wild type parental strains, we were able to determine that the presence of succinoglycan is crucial for plant to form infection threads. The production of succinoglycan by the rhizobia is regulated by a bacterial sensor protein on the surface of S. meliloti cells, which suggest S. meliloti has the ability to regulate the production of succinoglycan based on the signals it senses in its environment. The signals can be either plant products or changes of environment when S. meliloti cells colonized the surface of alfalfa root hairs cells. All together, our preliminary results suggest that the formation of infection threads could be the result of another signal exchange between S. meliloti and alfalfa. We are currently investigating the role of succinoglycan in eliciting the formation of infection threads inside the alfalfa root hairs with a grant from the National Institute of Health.

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