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United States Department of Agriculture

Agricultural Research Service

Research Project: GENETIC IMPROVEMENT OF FRUIT CROPS THROUGH FUNCTIONAL GENOMICS AND BREEDING Title: Transcriptomics of shading-induced and NAA-induced abscission in apple (Malus domestica) reveals a shared pathway involving reduced photosynthesis, alterations in carbohydrate transport and signaling and hormone crosstalk

Authors
item Zu, Hong -
item Dardick, Christopher
item Beers, Eric -
item Callahan, Ann
item Xia, Rui -
item Yuan, Rongcai -

Submitted to: Biomed Central (BMC) Plant Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 17, 2011
Publication Date: October 17, 2011
Citation: Zu, H., Dardick, C.D., Beers, E.P., Callahan, A.M., Xia, R., Yuan, R. 2011. Transcriptomics of shading-induced and NAA-induced abscission in apple (Malus domestica) reveals a shared pathway involving reduced photosynthesis, alterations in carbohydrate transport and signaling and hormone crosstalk. Biomed Central (BMC) Plant Biology. 11:138.

Interpretive Summary: Naphthaleneacetic acid (NAA) is widely used as an effective thinner in apple orchards. When applied shortly after fruit are produced, inferior young fruit drop so the remaining fruit will be larger and of better quality. However, the thinning results of NAA are inconsistent and difficult to predict, sometimes leading to excess fruit drop or insufficient thinning which are costly to growers. This unpredictability reflects our incomplete understanding of how NAA works to promote fruit drop. In this study, we compared NAA induced fruit drop with that caused by shading via gene expression profiling experiments performed on the fruit abscission zone (FAZ), sampled 1, 3, and 5 d after treatment. More than 700 genes with significant changes in transcript abundance were identified. While the differentially expressed gene sets for NAA and shading treatments shared only 25% identity, NAA and shading showed substantial similarity with respect to the classes of genes identified. Specifically, photosynthesis, carbon utilization, ABA and ethylene pathways were affected in both NAA and shading-induced young fruit abscission. Moreover, we found that NAA, similar to shading, directly interfered with leaf photosynthesis by repressing photosystem II efficiency within 10 minutes of treatment, suggesting that NAA and shading induced the same early responses due to reduced photosynthesis, which concurred with changes in hormone signaling pathways and caused fruit drop. This study provides a good platform for the further investigation of possible regulatory genes involved in the induction of young fruit abscission in apple, which will enable us to better understand the mechanism of fruit thinning and facilitate the selection of potential chemicals for the thinning programs in apple.

Technical Abstract: Naphthaleneacetic acid (NAA), a synthetic auxin analogue, is widely used as an effective thinner in apple orchards. When applied shortly after fruit set, some fruit abscise leading to improved fruit size and quality. However, the thinning results of NAA are inconsistent and difficult to predict, sometimes leading to excess fruit drop or insufficient thinning which are costly to growers. This unpredictability reflects our incomplete understanding of the mode of action of NAA in promoting fruit abscission. Here we compared NAA induced fruit drop with that caused by shading via gene expression profiling experiments performed on the fruit abscission zone (FAZ), sampled 1, 3, and 5 d after treatment. More than 700 genes with significant changes in transcript abundance were identified. Genes associated with ethylene, ABA, cell wall degradation, mitochondrial activity, glycolysis, lipid catabolism, secondary metabolism, abiotic stress, and programmed cell death were upregulated. On the other hand, there was down-regulation of genes related to photosynthesis, cell cycle, cell wall biosynthesis, carbon fixation, chromatin assembly, auxin transport, cytoskeleton function, and flower development. While the differentially expressed gene sets for NAA and shading treatments shared only 25% identity, NAA and shading showed substantial similarity with respect to the classes of genes identified. Specifically, photosynthesis, carbon utilization, ABA and ethylene pathways were affected in both NAA and shading-induced young fruit abscission. Moreover, we found that NAA, similar to shading, directly interfered with leaf photosynthesis by repressing photosystem II efficiency within 10 minutes of treatment, suggesting that NAA and shading induced some of the same early responses due to reduced photosynthesis, which concurred with changes in hormone signaling pathways and triggered fruit abscission. This study provides an extensive transcriptome study and a good platform for the further investigation of possible regulatory genes involved in the induction of young fruit abscission in apple, which will enable us to better understand the mechanism of fruit thinning and facilitate the selection of potential chemicals for the thinning programs in apple.

Last Modified: 11/20/2014
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