Natural variation in expression of genes associated with carotenoid biosynthesis and accumulation in cassava (Manihot esculenta Crantz) storage root

Authors: CARVALHO, LUIZ - Embrapa; DE ALMEIDA, JULIANA - Embrapa; AGUSTINI, MARCO - Embrapa; Anderson, James; VIERIA, EDUARDO - Embrapa; DE SOUZA, CLAUDIA - Universidade Federal Do Parana; CHEN, SONGBI - Chinese Academy Of Agricultural Sciences; SCHAAL, BARBARA - Washington University

Submitted to: BMC Plant Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/31/2016
Publication Date: 6/10/2016
Citation: Carvalho, L.J.C.B., Agustini, M.A.V,, Anderson, J.V., Vieria, E.A., de Souza, C.R.B., Chen, S., Schaal, B.A., Silva, J.P. 2016. Natural variation in expression of genes associated with carotenoid biosynthesis and accumulation in cassava (Manihot esculenta Crantz) storage root. Biomed Central (BMC) Plant Biology. 16:133. https://doi.org/10.1186/s12870-016-0826-0.
DOI: https://doi.org/10.1186/s12870-016-0826-0

Interpretive Summary: Naturally occurring color variation associated with carotenoid accumulation was observed in cassava storage root of 22 landraces from the Amazon. These carotenoids were analyzed to identify their diversity, determine their distribution in cassava storage root, and determine expression patterns for genes involved in carotenoid synthesis, cleavage and plastid division. Total ß-carotene was the major carotenoid type varying from 46% to 80% of the total carotenoid in cassava storage root. Lycopene was detected in landrace Cas51, which represents a pink colored cassava storage root, but it was not detected in landraces with yellow colored CSR. Landraces with white colored cassava storage root have five carotenoids types, while pink and yellow colored cassava storage roots have 1 to 17 different carotenoid types. Genes coding for enzymes associated with carotenoid biosynthesis in landraces IAC12, Cas51 and Cas62 revealed two putative mutations in the pathway. One of the mutations blocks the expression of LYCb in Cas51, causing increased accumulation of lycopene. The second mutation is related to down regulation of HYb in Cas62 causing increased accumulation of total b-carotene. Overall, total carotenoid accumulation was associated with tissue age, variation in color intensity, and consistency with the level of expression of genes coding for proteins related to plastid division. The nutritional value associated with high ß-carotene content may rank cassava as an important single source of retinol equivalent in a staple food crop. Further, landraces with increased levels of lutein could provide protection against the onset of age-related macular degradation, and landraces with increased lycopene could provide as an alternative source comparable to tomato.

Technical Abstract: Several groups have reported on massive accumulation of total carotenoids in cassava storage root (CSR). Naturally occurring color variation associated with carotenoid accumulation was observed in cassava (Manihot esculenta Crantz) storage root of landraces from Amazon. Here carotenoid profiles from High-Performance Liquid Chromatography with Diode-Array Detection (HPLC-DAD) were analyzed to identify the diversity of carotenoid types, determine their distribution in CSR during secondary growth, and monitor abundance of transcripts coding for enzymes involved in carotenoid synthesis, cleavage and plastid division by deploying two complementary technologies. Total ß-carotene (all-E ß-carotene, 9-Z and 13-Z isomers) was the major carotenoid type varying from 46% to 80% of the total carotenoid in CSR. No peak corresponded to a-carotene, but variable amounts of lutein (a a-ring xanthophyll) were detected. Xanthophylls (a-ring and ß-ring) content preferentially accumulated greater amounts of b-ring violaxanthin than a-ring xanthophyll. Lycopene detected in landrace Cas51, representing pink colored CSR, was not detected in the yellow colored CSR landraces. White storage root has five carotenoids types, while in pink and yellow CSR 1 to 17 different types were observed. Transcript profiles of genes coding for enzymes of carotenoid synthesis and cleavage, and plastid division were accessed by global transcript analysis and qRT-PCR. Abundance of transcripts coding for enzymes associated with carotenoid biosynthesis were consistent with carotenoid composition of contrasting HPLC-DAD profiles for IAC12, Cas51 and Cas62, revealing putative mutations in the pathway. Eight genes coding for proteins regulating plastid division were also consistent with differences in b-carotene accumulation. Genetic analysis based on pattern association of gene expression as well as carotenoids HPLC-DAD led to the identification of highly diverse carotenoid types and two putative mutations in cassava storage root. One of the mutations blocks the expression of LYCb in Cas51, causing increased accumulation of lycopene. The second is related to down regulation of HYb in Cas62 causing increased accumulation of total b-carotene. Total carotenoid accumulation revealed spatial and temporal pattern association with tissue age, variation in color intensity, and consistency with the level of expression of genes coding for proteins related to plastid division.