A molecular approach to identify components of
photoperiod induced dormancy in alfalfa (Medicago sativa L.)
Diane Luth1, Randy C. Shoemaker2,
and E. Charles Brummer1
1 Agronomy Department, Iowa
State University, Ames IA
50011-1010
2 USDA-ARS, Corn Insect and Crop Genetics Research
Unit,
Agronomy
Department, Iowa State University, Ames IA
50011-1010
Alfalfa plants characterized as fall dormant react
to changes in daylength and temperature during the onset of autumn-like
conditions. The premature dormancy
results in reduced yields due to growth reduction in late summer and early
fall. Fall dormant plants are also
slower to resume shoot growth in the spring and following harvest in summer.
Therefore breeding alfalfa cultivars with less fall dormancy would be
desirable. Dormancy is regulated by the
interactions of environmental factors including photoperiod and temperature,
the physiological status of the plant, and the plant genotype. The mechanisms controlling dormancy in
alfalfa are not well understood, nor are the ensuing effects on winter
survival. We have undertaken 2
approaches to study dormancy related gene expression focusing on
photoperiod: RNA profiling and cDNA
subtractive hybridization. For the RNA
profiling approach, cDNA libraries were constructed from dormant and nondormant
genotypes of Medicago sativa subsp. sativa and falcata grown under dormancy inducing and noninducing photoperiod
regimes at a constant temperature.
Microarrays will be made from the isolated cDNAs and used to analyze
photoperiod induced gene expression in alfalfa genotypes differing in dormancy
response. The mRNA populations used to measure transcript abundance include
genotypes grown under both natural field and controlled (photoperiod and
temperature) conditions. Expression
will be determined for different tissue types in the plants. Concurrently we
are also pursuing a subtractive cDNA subtractive approach utilizing
Wisfal–6. This procedure allows us to
equalize transcript abundance and subtract out transcripts expressed in both
inducing and non-inducing regimes, increasing the possibility of obtaining
differentially expressed rare transcripts.
The differentially expressed genes from the RNA profiling approach and the
cDNA subtractive studies will be sequenced and mapped. The information from alfalfa will then be
used to investigate synteny among photoperiod and dormancy associated genes in
soybean and Arabidopsis.