Submitted to: Journal of Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/4/2008
Publication Date: 3/1/2009
Citation: Yue, B., Cai, X., Vick, B.A., Hu, J. 2009. Genetic Characterization and Molecular Mapping of a Chlorophyll Deficiency Gene in Sunflower (Helianthus annuus). Journal of Plant Physiology. 166:644-651. Interpretive Summary: Leaf color variation is one of the common visible morphological traits in higher plants and the change in leaf color is usually caused by nuclear genes involved in chlorophyll metabolism. This paper reports the genetic characterization and molecular mapping of a major gene conferring leaf color in sunflower. The 172 F2 plants were derived from a cross between two breeding lines, a light green leaf line from Australia and a normal green leaf line from China. Genetic analysis revealed that a single gene (lg for light green) is responsible for the leaf color phenotype. The segregation of normal green and light green leaves fit the monogenic ratio. Measurement of chlorophyll with a spectrophotometer revealed that the difference in leaf color resulted from chlorophyll content variation among the plants. We successfully mapped the lg gene onto linkage group 10 of the public sunflower SSR map. In sunflower, a previous study revealed a significant and positive correlation between chlorophyll content and net photosynthesis. The identification of a major gene controlling chlorophyll contents in sunflower offers the opportunity to achieve a higher photosynthesis level to increase biomass and grain yield production through genetic manipulation in the future.
Technical Abstract: A major gene controlling leaf color (lg for light green versus normal green) of sunflower was identified and mapped in an F2 population derived from a cross between two breeding lines. All 20 F1 plants from the cross had normal green leaf color and the segregation of 172 plants in an F2 population fit the monogenic ratio of 130 green-leafed to 42 light green-leafed plants (Chi squared(3:1)=0.03, p>0.9). The greenness degree of leaf color of individual F2 plants was measured with a hand-held chlorophyll content meter. The greenness degree varied from 30.2 to 41.6 and 15.3 to 27.1 within the normal green- and light green-leafed groups, respectively. These results indicated that leaf color is a monogenic trait with normal green dominant over light green. Measurement of chlorophyll with a spectrophotometer revealed that the difference in leaf color resulted from chlorophyll content variation among the plants. The contents of chlorophyll a, chlorophyll b, and total chlorophyll in the green-leafed lines were 71.9%, 115.0%, and 79.4% higher than those in the light green-leafed lines, respectively. Genetic mapping with molecular markers positioned the lg gene to linkage group 10 of sunflower. A previously mapped SSR marker, ORS 595, cosegregated with the lg locus, and a TRAP marker, B26P17ga5-300, was linked to the lg locus with a genetic distance of 4.2 cM. The markers tightly linked to the locus will serve as the starting point to isolate this gene through map-based cloning.