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United States Department of Agriculture

Agricultural Research Service

Research Project: Improving bioenergy and forage plants and production systems for the central U.S.

Location: Grain, Forage & Bioenergy Research

Title: Switchgrass (Panicum virgatum L) flag leaf transcriptomes reveal molecular signatures of leaf development, senescence, and mineral dynamics

Authors
item Palmer, Nathan
item Donze-Reiner, Teresa -
item Horvath, David
item Heng-Moss, Tiffany -
item Waters, Brian -
item Tobias, Christian
item Sarath, Gautam

Submitted to: Functional and Integrative Genomics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 16, 2014
Publication Date: N/A

Interpretive Summary: Perennial grasses such as switchgrass are being developed as sources of biomass for the biofuel sector. The perenniality of these plants is partially dependent on the return of nutrients from the above ground tissues to the below ground tissues. This yearly process allows the sustainable harvest of above ground biomass to produce biofuels. The molecular mechanisms underlying this complex web of plant behavior is not known, but has been linked to the onset of senescence (death) of the stems and leaves, particularly the last produced leaf, called the flag leaf. In this study we have evaluated the molecular changes that accompany flag leaf development across a growing season in field grown plants. RNA extracted from the leaves was analyzed by next- generation sequencing methods. The vast amount of data yielded by sequencing was analyzed using tools in bioinformatics to develop a molecular road-map of switchgrass flag leaf development. Many genes that could be important to triggering leaf senescence and nutrient transfer from the shoots to the roots were identified. This study provides a good resource for future investigations of switchgrass growth and development.

Technical Abstract: We provide the first comprehensive transcriptomic inspection of switchgrass flag leaf development. Flag leaves were collected from field grown switchgrass plants at five plant developmental stages: heading, anthesis, early and late seed development, and at physiological maturity and analyzed by RNA-Seq. On average approximately 45.6 M 100 bp single-end reads were obtained for each sample of which almost 78% were mapped to annotated gene models present in the switchgrass genome. Chlorophyll content increased from the first harvest at heading and began to decline after anthesis and was significantly lower at the last harvest date, indicating that leaf senescence had been initiated. Changes in chlorophyll content were mirrored in the expression levels of genes associated with chlorophyll biosynthesis and degradation respectively, providing a molecular roadmap for switchgrass flag leaf ontogeny. Using this roadmap, it was possible to associate the expression profiles for a large number of other genes to the developmental stages of flag leaves. Gene-expression profiles were used to identify transcriptional networks that appear to function at different stages of leaf development. Several genes that could exert a control on the remobilization of nutrients from the senescing flag leaves to the rhizomes have been identified. Determining how aerial senescence is integrated with the onset of dormancy in the rhizomes is among the important unknowns in switchgrass biology. Data presented here provide an important resource for these future studies.

Last Modified: 10/1/2014
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