Progress 01/01/09 to 12/31/09
Outputs
OUTPUTS: We continued our research on the regulatory mechanisms underlying leaf yellowing processes. Leaf's primary function is photosynthesis. At the onset of leaf yellowing, the leaf loses its photosynthetic capability, resulting in limitation of crop yield, reduced nutritional values of vegetables and feeds, losses of horticultural crops after harvest, and development of fungal diseases. Postharvest fungal pathogens often produce toxins that render our food unsafe. Our objectives are to understand the yellowing processes at the molecular and genetic levels, and based on our findings, and based on our findings to devise means to slow down or inhibit the processes for agricultural improvement. Another aspect of our research is to understand the molecular events associated with apple fruit thinning. For the past year, we have continued making significant progresses towards our goals. Briefly, we have confirmed that the master regulator we previously cloned plays a key role in controlling leaf yellowing processes in soybean. We designed a strategy to suppress the master regulator, resulting in a new soybean germplasm that displays a significantly delay yellowing phenotype and thus dramatically enhanced soybean seed yield and biomass accumulation. A patent application on our discovery has been granted/approved by US PTO. Several biotech firms have signed contracts with Cornell to commercialize our findings. We also identified some target genes of the senescence regulator and have characterized one of them in details, which will help us to understand how senescence is regulated at the molecular level, which may lead to new technology for manipulating senescence for agricultural improvement. PARTICIPANTS: Not relevant to this project. TARGET AUDIENCES: Not relevant to this project. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
Our continued research effort on soybean has provided a paradigm of translational plant biology. We initially found the master regulator of leaf yellowing from a model system called Arabidopsis. We used this knowledge gained from Arabidopsis to identify the counterpart in soybean and subsequently to manipulate this master regulator in soybean, resulting in a new soybean germplasm with significantly enhanced seed yield and biomass accumulation. Seed yield is a major factor effecting profitablity of soybean farming but the yield has reached a point called yield plateau. Our research has overcome this plateau. In addition to enhanced yield, we also analyzed the chemical and nutritional components of the seeds and found that there are no changed; that is, the seeds produced by our new germplasm are just as good as parental (wild type) seeds. In addition to soybean, we have expanded our research to other agronomic and horticultural crops (maize, alfalfa, and turfgrass). We believe that our findings can be widely applied to a wide spectrum of crops for enhanced yield and biomass accumulation, and for improved postharvest longevity of vegetables and flowers. In addition, our findings of target genes of the senescence regulator have shed significant lights on how the senescence is regulated.
Publications
- Zhou, C., Cai, Z., Guo, Y. and Gan, S. (2009) An Arabidopsis mitogen-activated protein kinase cascade, MKK9-MPK6, plays a role in leaf senescence. Plant Physiology 150: 167-177.
- Ponce-Valadez, M., Fellman, S.M., Giovannoni, J., Gan, S. and Watkins, C.B. (2009) Differential fruit gene expression in two strawberry cultivars in response to elevated CO2 during storage revealed by a heterologous fruit microarray approach. Postharvest Biology and Technology 51: 131-140.
- Zhou, C. and Gan, S. (2009) Senescence. In: Plant Developmental Biology: Biotechnological Perspectives (ed by E. C. Pua and M. R. Davey). pp151-169, Springer.
|
Progress 10/01/07 to 09/30/08
Outputs
OUTPUTS: One important aspect of our research is to decipher the regulatory mechanisms underlying leaf yellowing processes. Leaf's primary function is photosynthesis. At the onset of leaf yellowing, the leaf loses its photosynthetic capability, resulting in limitation of crop yield, reduced nutritional values of vegetables and feeds, losses of horticultural crops after harvest, and development of fungal diseases. Postharvest fungal pathogens often produce toxins that render our food unsafe. Our objectives are to understand the yellowing processes at the molecular and genetic levels, and based on our findings, and based on our findings to devise means to slow down or inhibit the processes for agricultural improvement. Another aspect of our research is to understand the molecular events associated with apple fruit thinning. For the past year, we have continued making significant progresses towards our goals. Briefly, we have confirmed that the master regulator we previously cloned plays a key role in controlling leaf yellowing processes in soybean. We designed a strategy to suppress the master regulator, resulting in a new soybean germplasm that displays a significantly delay yellowing phenotype and thus dramatically enhanced soybean seed yield and biomass accumulation. Several biotech firms have signed contracts with Cornell to commercialize our findings. We have also discovered genes that are closely associated with fruit thinning, and we are investigating how these genes function so that we will be able to manipulate them for much improved apple fruit thinning in the future. PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Our research on soybean represents a paradign of translational plant biology. We initially found the master regulator of leaf yellowing from a model system called Arabidopsis. We used this knowledge gained from Arabidopsis to identify the counterpart in soybean and subsequently to manipulate this master regulator in soybean, resulting in a new soybean germplasm with significantly enhanced seed yield and biomass accumulation. Seed yield is a major factor effecting profitablity of soybean farming but the yield has reached a point called yield plateau. Our research has overcome this plateau. In addition to enhanced yield, we also analyzed the chemical and nutritional components of the seeds and found that there are no changed; that is, the seeds produced by our new germplasm are just as good as parental (wild type) seeds. In addition to soybean, we have expanded our research to other agronomic and horticultural crops (maize, alfalfa, and turfgrass). We believe that our findings can be widely applied to a wide spectrum of crops for enhanced yield and biomass accumulation, and for improved postharvest longevity of vegetables and flowers.
Publications
- Zhou, C., Lakso, A., Robinson, T. and Gan, S. (2008). Isolation and characterization of genes associated shade-induced apple abscission. Molecular Genetics and Genomics 280: 83-92.
- Ponce-Valadez,M., Fellman,S., Giovannoni, J., Gan, S. and Watkins, C. B. (2008) Differential fruit gene expression in two strawberry cultivars in response to elevated CO2 during storage revealed by a heterologous fruit microarray approach. Postharvest Biology and Technology (doi:10.1016/j.postharvbio.2008.08.001)
|
Progress 01/01/07 to 12/31/07
Outputs
Our research continued focusing on the regulatory mechanisms underlying leaf yellowing processes. In an agricultural setting, leaf yellowing is not desirable for the following reasons: (1) leaf yellowing limits crop yield and biomass accumulation; (2) leaf yellowing causes significant loss of vegetables during storage, transportation and on shelves, (3) leaf yellowing causes loss of nutritional values because proteins, antioxidants and other useful nutrients are degraded; (4) leaf yellowing may render our vegetables unsafe because yellowing leaves become much more vulnerable to pathogen attach, especially fungal pathogens (some of which produce toxins). Our goal has been to understand the yellowing processes and to devise means to delay or slow down the processes for agricultural improvement. For the past year, we have made significant progress towards our goal. Briefly, we have identified some key regulators of the yellowing processes and, by manipulating one of the
key regulators, we have generated soybean plants in which leaf yellowing is significantly delayed and the soybean seed yield appeared to be increased for more than 40%. Cornell has filed a patent application on our discovery (PCT/US2007/065321, officially filed on March 28, 2007). Our findings have also attracted attentions/interests from several biotech companies, and may spin off a biotech startup company in upstate of New York.
Impacts
One of our important findings is the discovery of a transcription factor gene called NAP. We initially discovered this gene in Arabidopsis, a model system. When this gene is knocked out, leaf yellowing processes are delayed for more than 10 days. The leaves are photosynthetically active. Based on this finding in Arabidopsis, we extended our research to agronomic and horticultural crops and found this gene exists in all crop and other non-crop plants. In other words, this gene represents a universal mechanism by which leaf yellowing is controlled in all plant species. For example, when this gene was suppressed in soybean, the soybean plants displayed a more than 10-day-delay in leaf senescence, resulting in at least 40% increase in seed yield as revealed in our greenhouse experiments. This finding will overcome the plateau of yield in many crops and will significantly prolong the postharvest longevity of many vegetable and floricultural crops. Our research represents a
paradigm of plant translational researches. In addition, the PI edited a major academic book entitled SENESCENCE PROCESSES IN PLANTS, a volume of Annual Plant Reviews that was published by Blackwell Publishing. This book is of significance in plant senescence research.
Publications
- Gan, S. (ed). 2007. Senescence Processes in Plants. Blackwell Publishing (UK), ca 352. March.
- Gan, S. 2007. Mitotic senescence in plants. In: Senescence Processes in Plants (Gan S., ed). Blackwell Publishing, pp. 1-11. March.
- Guo, Y. and Gan, S. 2007. Genetic manipulation of leaf senescence. In: Senescence Processes in Plants (Gan S., ed). Blackwell Publishing, pp.304-322. March.
|
Progress 01/01/06 to 12/31/06
Outputs
We have continued to make significant progress in our research on senescence for the past year. Briefly, we have identified a master regulator of leaf senescence named AtNAP from Arabidopsis. This regulator plays a key role in promoting leaf senescence in not only Arabidopsis but also many other plant species including such crops as rice, wheat, barley, maize, soybean, kidney bean, tomato. In other words, this appears to be a universal regulator of leaf senescence, which has led to a new biotechnological approach to manipulation of leaf senescence. We have also found an important gene that controls senescence in harvested leaves only. This finding may lead to new strategies for controlling senescence in horticultural products during storage, transportaion and on shelf.
Impacts
1. The identification of a master regulator of senescence has led to the new biotechnology for manipulating leaf senescence in various crops, resulting in significantly enhanced yield and bioenergy production. 2. The discovery of a gene specifically regulating senescence in detached leaves may have a great potential in controlling senescence in harvested horticultural crops.
Publications
- Guo, Y, and Gan, S. 2006 AtNAP, A NAC family transcription factor, has an important role in leaf senescense. The Plant Journal 46: 601-612.
- Swartzberg, D., Dai, N., Gan, S., Amasino, R., and Granot, D. 2006 Effects of cytokinin production under two SAG promoters on senescence and development of tomato plants. Plant Biology 8: 579-586.
|
Progress 01/01/05 to 12/31/05
Outputs
Leaf senescence is an integral part of plant development that involves cell death and nutrient recycling. It is a distinct process that differs significantly from many other developmental processes that involves primarily cell division, differentiation, and/or enlargement. Leaf senescence has a significant impact on agriculture because leaf senescence (1) limits crop yield and forest biomass accumulation, (2) contributes to much of postharvest loss of vegetable crops during storage, transportation and on shelves, (3) devalues ornamental plants. The goal of our research has been to decipher the molecular regulatory mechanisms underlying leaf senescence, and to devise ways to manipulate senescence process for agricultural improvement. To approach this goal, we have employed molecular, genetic and genomic strategies to analyze the senescence process, and we have continued making significant progress toward achieving our goal. For the past year, we focused on the
darkness-induced postharvest senescence because it is an important problem that most of horticultural crops are encountering. Specifically, we performed bioinformatic analysis of darkness-induced vs. natural leaf senescence in Arabidopsis. Taking advantage of rich microarray data available, we analyzed the gene expression profiles in dark-induced leaf senescence vs. natural leaf senescence (as well as other programmed cell death) in Arabidopsis. We found that there were 2081 genes whose transcript levels were increased 3 times or more in dark-induced senescing leaves, compared with 1481 genes in natural senescing leaves and 1609 genes in programmed cell death of suspension cells. Dark-induced senescence and natural leaf senescence shared 520 genes. At least 1340 genes were expressed in dark-induced senescing leaves only. These data suggest that dark-induced leaf senescence is more complex than other two forms of cell death analyzed. A manuscript describing this analysis and other data
is in preparation. We also revealed that WRKY75, a transcription factor, may play an important role in darkness-induced senescence in detached leaves. We found WRKY75 transcription factor gene was specifically expressed during natural and dark-induced leaf senescence in Arabidopsis. T-DNA knockout (KO) lines displayed no changes in growth and development (including natural leaf senescence). However, senescence in detached leaves of KO plants under darkness was significantly delayed compared that in wild type plants. Senescence induced by plant hormones such as ABA, ethylene, JA or SA was not altered in the KO plants. We performed a complementation test and found that a copy of the wild-type WRKY75 gene, when transferred into the KO plants, could restore the KO phenotype to wild type. These data strongly suggest that WRKY75 is a key regulator of dark-induced senescence in detached leaves. We are currently investigating if WRKY75 is sufficient to cause darkness-induced leaf
senescence.
Impacts
These findings shed some light on the regulation of darkness-induced postharvest leaf senescence at the molecular level, and provide new strategy for delaying darkness-induced leaf senescence.
Publications
- Gan, S. 2005. The hormonal regulation of senescence. In Plant Hormones: Biosynthesis, Signal Transduction, Action (P.J. Davies ed). Kluwer Academic Publishers, pp. 561-581.
- Guo, Y. and Gan, S. 2005. Leaf senescence: signals, execution, and regulation. Current Topics in Developmental Biology 71:83-112.
- Gan, S. 2005. Molecular genetic analysis of senescence. International Conference on the Frontiers of Plant Molecular Biology, p.53.
- Gan, S. 2005. Proceedings of the 4th Korea-USA Joint Seminar on Plant Molecular Genetics and Breeding, p.25.
- Guo, Y. and Gan, S. 2005. The transcription factor AtMYB2 regulates whole plant senescence through cytokinin anabolic pathway. 16th International Conference on Arabidopsis Research, Abstract #324.
|
Progress 01/01/04 to 12/31/04
Outputs
Leaf senescence is the last stage of leaf development. It is achieved by a massive operation of programmed cell death. Changes in gene expression have been believed to be the driving force for the senescence process. There are at least two sets of genes whose expression is altered at the onset of and during leaf senescence. One set is those genes that are upregulated with an increased level of transcripts and the other set is those genes whose transcript abundance is reduced. Some of the downregulated genes may be senescence inhibitors while some (if not all) of the upregulated genes may be senescence promotors. For the past year, we have made significant progresses in our research toward our molecular cloning and characterization of these two sets of genes. Specifically, we investigated the function of some senescence-promoting genes, especially those transcription factor genes. For example, we have shown that SAG101, a NAC family transcription gene, plays an
important role in leaf senescence because leaf senescence is significantly delayed when it is knocked out, while inducible overexpression of the gene causes precocious senescence. In addition to the upregulated genes, we have also developed a soma genetics strategy. By using this innovative strategy, we have identified a novel gene encoding a small peptide. The expression of this peptide is sufficient to suppress leaf senescence. We are currently using the soma genetics system to comb the entire genome of tobacco (a relative of tomato and potato) for senescence-inhibiting genes. The genes identified from tobacco shall be readily used for manipulating leaf senescence in agronomical and horticultural crops.
Impacts
The breakthrough findings provide new insights into the regulation of leaf senescence at the molecular level. The new soma genetics system we have developed will become a powerful tool for agriculture biotechnology research.
Publications
- Guo, Y., Cai, Z. and Gan, S. 2004. Transcriptome of Arabidopsis leaf senescence. Plant, Cell & Environment 27:521-549.
- He, Y. and Gan, S. 2004. A novel zinc finger protein with a proline-rich domain mediates ABA-regulated seed dormancy in Arabidopsis. Plant Molecular Biology 54:1-9.
|
Progress 01/01/03 to 12/31/03
Outputs
Leaf senescence is a complex developmental process during which essential nutrients are recycled. In order to unravel the biochemical pathways and regulatory mechanisms that underlie this process, it would be valuable to examine the transcriptome associated with leaf senescence. Accordingly, an Arabidopsis thaliana leaf senescence cDNA library with approximately 104 recombinant clones was subjected to large-scale single-pass sequencing. Approximately 6,200 expressed sequence tags (ESTs) were obtained, corresponding to 2,491 unique genes. These included 134 genes encoding transcription factors and 182 genes whose products are components of signal transduction pathways, such as the mitogen-activated protein kinase (MAPK) cascades. A total of 116 of these genes are predicted to be involved in protein turnover, including 75 genes associated with the ubiquitin-proteasome pathway and 35 proteinases. Many of the genes are predicted to encode transporters for ions, amino
acids and sugars, consistent with the substantial nutrient recycling during leaf senescence. In addition, this study revealed ESTs for 98 annotated genes for which ESTs did not previously exist and 46 novel transcribed units that have not previously been annotated in the Arabidopsis genome. Approximately one third of the 2,491 genes are predicted to encode proteins with unknown functions. The genes are distributed evenly on the 5 chromosomes. This work has been accepted for publication in Plant, Cell & Environment (March issue, 2004).
Impacts
The research finding represents a milestone in the senescence research field. It provides a global view on the senescence process that will allow us to manipulate senescence for agricultural improvement.
Publications
- Gan, S. 2003. Mitotic and postmitotic senescence in plants. Science's SAGE KE ) http://sageke.sciencemag.org/cgi/content/full/sageke;2003/38/re7
|
|