UBC Theses and Dissertations
Development of genetic resources and functional analysis of betalains in Amaranthus species Adhikary, Dinesh
Amaranth is an ancient crop in which interest is being renewed, due to its adaptability, stress tolerance, and nutritional value. The grain amaranths (Amaranthus caudatus L., A. cruentus L., A. hypochondriacus L.) are grown primarily for their seeds, which are protein-rich pseudocereals. Some species of amaranths are also major noxious weeds (e.g A. palmeri). Many members of the amaranth family (Amaranthaceae) produce red (betacyanin) or yellow (betaxanthin) betalain pigments, which are chemically distinct from the anthocyanins responsible for red pigmentation. My objective was to develop resources that will aid in further research and improvement of grain amaranths, and to use these resources to investigate the ecological significance of betalains. I produced the first major catalog of amaranth genes by assembling transcriptomes from eight tissues of A. hypochondriacus cv. Plainsman, the major commercial cultivar. These tissues included seeds and embryos at three stages of development. Reverse genetics techniques are useful to induce a loss-of-function and therefore infer gene function. I succeeded in establishing the first reverse genetics protocol for amaranths, using virus-induced gene silencing (VIGS). I used VIGS to target putative betalain biosynthetic genes AtriCYP76AD1 and AtriPPO1 in an intensely red-pigmented amaranth species, A. tricolor. VIGS of AtriPPO1 resulted in severe necrosis. VIGS of AtriCYP76AD1 resulted in a nearly complete loss of detectable red pigment in some tissues. Protection from UV-induced damage is one of the roles that has been proposed for betalains. To test this hypothesis, I compared UV responses in a red-pigmented A. tricolor variety with green tissues in VIGS treated plants of the same variety, and with a green variety of A. tricolor. Following UV exposure, the red and green tissues showed similar responses in photosynthetic activity, oxidative damage, and in the production of markers of UV-B stress. However, the red tissues uniquely showed an increase in photosynthetic pigments under UV-B treatment, whereas the photosynthetic pigments decreased in green tissues. Thus, although our experiment did not provide any evidence that betacyanins are UV-B or ROS-protective, the presence of betacyanin was correlated with a differential response of photosynthetic pigments, perhaps due to filtering of specific visible wavelengths.
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