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CaGLK2 regulates natural variation of chlorophyll content and fruit color in pepper fruit

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We provide multiple evidences that CaGLK2 underlies a quantitative trait locus controlling natural variation in chlorophyll content and immature fruit color of pepper via modulating chloroplast compartment size.


Pepper fruit quality is attributed to a variety of traits, affecting visual appearance, flavor, chemical composition and nutritional value. Among the quality traits, fruit color is of primary importance because the pigments that confer color are associated with nutrition, health and flavor. Although gene models have been proposed for qualitative aspects of fruit color, large natural variation in quantitative pigment content and fruit color exists in pepper. However, its genetic basis is largely unknown which hampers its utilization for plant improvement. We studied the role of GLK2, a GOLDEN2-like transcription factor that regulates chloroplast development in controlling natural variation for chlorophyll content and immature fruit color of pepper. The role of GLK2 in regulating fruit development has been studied previously in tomato using ectopic expression and the uniform ripening mutant analyses. However, pepper provides a unique opportunity to further study the function of this gene because of the wide natural variation of fruit colors in this species. Segregation, sequencing and expression analyses indicated that pepper GLK2 (CaGLK2) corresponds to the recently reported pc10 QTL that controls chloroplast development and chlorophyll content in pepper. CaGLK2 exerts its effect on chloroplast compartment size predominantly during immature fruit development. We show that the genetic background, sequence variation and expression pattern confer a complex and multi-level regulation of CaGLK2 and fruit color in Capsicum. The positive effect on fruit quality predominantly at the green stage conferred by CaGLK2 can be utilized to breed green pepper varieties with improved nutritional values and taste.

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This research was supported by Research Grant No. IS-4752-14 R from BARD, the United States-Israel Binational Agricultural Research and Development Fund. We thank Saadia Nahon for technical support, Eduard Belausov for assistance with confocal microscopic analyses, Dr. Arthur Schaffer and Lena Yeselson for sugar analyses. We thank Dr. Eyal Fridman (Hebrew University) for Ph.D. guidance of Arnon Brand. We thank Dr. Jose Luiz Luna and Dr. Kraig Kraft, Aguascalientes, Mexico for providing the C. annuum var. glabriusculum lines for this work.

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The authors declare no conflict of interests.

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Correspondence to Ilan Paran.

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Communicated by Carlos F. Quiros.

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Brand, A., Borovsky, Y., Hill, T. et al. CaGLK2 regulates natural variation of chlorophyll content and fruit color in pepper fruit. Theor Appl Genet 127, 2139–2148 (2014).

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