Agave as a model CAM crop system for a warming and drying world

Abstract

As climate change leads to drier and warmer conditions in semi-arid regions, growing resource-intensive C3 and C4 crops will become more challenging. Such crops will be subjected to increased frequency and intensity of drought and heat stress. However, agaves, even more than pineapple (Ananas comosus) and prickly pear (Opuntia ficus-indica and related species), typify highly productive plants that will respond favorably to global warming, both in natural and cultivated settings. With nearly 200 species spread throughout the U.S., Mexico, and Central America, agaves have evolved traits, including crassulacean acid metabolism (CAM), that allow them to survive extreme heat and drought. Agaves have been used as sources of food, beverage, and fiber by societies for hundreds of years. The varied uses of Agave, combined with its unique adaptations to environmental stress, warrant its consideration as a model CAM crop. Besides the damaging cycles of surplus and shortage that have long beset the tequila industry, the relatively long maturation cycle of Agave, its monocarpic flowering habit, and unique morphology comprise the biggest barriers to its widespread use as a crop suitable for mechanized production. Despite these challenges, agaves exhibit potential as crops since they can be grown on marginal lands, but with more resource input than is widely assumed. If these constraints can be reconciled, Agave shows considerable promise as an alternative source for food, alternative sweeteners, and even bioenergy. And despite the many unknowns regarding agaves, they provide a means to resolve disparities in resource availability and needs between natural and human systems in semi-arid regions.

Review and in silico analysis of fermentation, bioenergy, fiber, and biopolymer genes of biotechnological interest inAgaveL. for genetic improvement and biocatalysis

“…As described, Agave plants avoid physiological damage from drought and high temperatures by nocturnal assimilation of carbon dioxide (CO 2 ), thick waxy cuticles, low stomata density, and succulent leaves. The latter two adaptations allow continuous flow into the chlorenchyma of water stored in the parenchyma during periods of water shortage, conferring plants with resistance to over 7 years of water scarcity …”

“…Fructans are classified according on the linkage between fructosyl residues and glucose in six groups: inulins, with β‐(2 → 1) glycosidic linkages, characteristic of Asteraceae such as Cichorium spp. (chicory) and Helianthus tuberosus L. (Jerusalem artichoke); levans with fructosyl residues linked by β‐(2 → 6) linkages, abundant in Poaceae such as Phleum pretense L. (timothy grass) and Lolium perenne L. (perennial ryegrass); graminans with both β‐(2 → 1) and β‐(2 → 6) linkages, found in wheat and barley, and in some members of Asparagales; inulin neoseries with β‐(2 → 1) linkages, characteristic of onion and asparagus; levan neoseries with both β‐(2 → 1) and β‐(2 → 6) linkages, found in oats and some species of Poales; and agavins with β‐(2 → 1) and β‐(2 → 6) linkages in branched graminan fructans and neo‐fructans, characteristic of the genera Agave and Dasylirion Zucc …”

“…By means of HPLC, HPAEC‐PAD, MALDI‐TOF‐MS, and GC‐MS, fructans with β(2 → 1) and β(2 → 6) linkages have been found in A. tequilana , A. potatorum , A. angustifolia, A. fourcroydes, A. cantala, and A. deserti with average degree of polymerization (DP) values ranging from DP 3 to DP 30 . Fructans with low DP values (DP 3‐DP 6) can be used as prebiotics and fructans with DP values above 15 are required for several fermentative processes for production of alcoholic beverages and bioethanol from must of several species of Agave . Added to these claim for searching new species with higher content of fructans and adequate PD values for different biotechnological purposes, fructans are demanded by the food industry as food texture and consistence improvers, for their probiotic value, and as immune system stimulators .…”

“…CAM photosynthesis and low contents of lignin are also advantageous for using Agave plants as energy crops for production of second‐generation biofuels by enzymatic digestion of lignocellulosic plant material . Finally, residues from the tequila industry might be a source of fuel and for generating electricity …”

“…The American plant genus Agave L. includes over 200 species, of which 166 are distributed throughout México . The crassulacean acid metabolism (CAM), superficial root system, and succulent leaves with thick, waxy cuticle of the species of Agave provides them with adaptive advantage in an ample range of geographical zones, as a result of their resistance to abiotic and biotic environmental factors including drought, salinity, extreme temperatures, and pathogens . These genetic, morphological, and physiological skills of economically important crops in the genus Agave make its species promising for minimizing the risk of losses as a result of the global climate change in present and future biotechnological applications .…”