Modifying crops to increase cell wall digestibility

Abstract

Improving digestibility of roughage cell walls will improve ruminant animal performance and reduce loss of nutrients to the environment. The main digestibility impediment for dicotyledonous plants is highly lignified secondary cell walls, notably in stem secondary xylem, which become almost non-digestible. Digestibility of grasses is slowed severely by lignification of most tissues, but these cell walls remain largely digestible. Cell wall lignification creates an access barrier to potentially digestible wall material by rumen bacteria if cells have not been physically ruptured. Traditional breeding has focused on increasing total dry matter digestibility rather than cell wall digestibility, which has resulted in minimal reductions in cell wall lignification. Brown midrib mutants in some annual grasses exhibit small reductions in lignin concentration and improved cell wall digestibility. Similarly, transgenic approaches down-regulating genes in monolignol synthesis have produced plants with reduced lignin content and improved cell wall digestibility. While major reductions in lignin concentration have been associated with poor plant fitness, smaller reductions in lignin provided measurable improvements in digestibility without significantly impacting agronomic fitness. Additional targets for genetic modification to enhance digestibility and improve roughages for use as biofuel feedstocks are discussed; including manipulating cell wall polysaccharide composition, novel lignin structures, reduced lignin/polysaccharide cross-linking, smaller lignin polymers, enhanced development of non-lignified tissues, and targeting specific cell types. Greater tissue specificity of transgene expression will be needed to maximize benefits while avoiding negative impacts on plant fitness.cauliflower mosiac virus (CaMV) 35S promoter.

Senescence, dormancy and tillering in perennial C4 grasses

“…It is also possible to compromise switchgrass plant fitness (winter survival) by repeated selection for increased in vitro dry matter forage digestibility (as a proxy for ruminant digestion; [38]) in northerly adapted populations as a consequence of lowering lignin content of the biomass [39]. Although such selection did not lead to changes in the timing of plant developmental responses, such as green-up and flowering dates, populations with lower plant lignin had greater winter kill.…”

Transgenic switchgrass (Panicum virgatum L.) targeted for reduced recalcitrance to bioconversion: a 2‐year comparative analysis of field‐grown lines modified for target gene or genetic element expression

“…It has increasing genetic resources (JGI Phytozyme 2016) and the strong potential to be grown with low inputs (McLaughlin and Adams Kszos, 2005; U.S. Department of Energy – Office of Biological and Environmental Research 2014). Understanding factors that influence recalcitrance is critical to improve switchgrass and other feedstocks as bioenergy fuel sources and multiple cell wall biosynthesis gene targets for improving plants via breeding and biotechnology have been discussed (Jung et al ., 2012). …”

Fatty acid profile and nutritive value of quinoa (Chenopodium quinoa Willd.) seeds and plants at different growth stages

“…Improta and 22 Kellens (2001) reported that processing (polishing or washing) of quinoa prior to feeding, or 23 diluting the quinoa with some other available feed are viable options that can be considered for 24 improving performance of broilers when quinoa is a major component of the diet. 2 The herbage samples were immediately dried in a forced-draft air oven to a constant weight 3 and the drying temperature was set at 65°C. The samples were then brought to air temperature, 4 weighed, ground in a Cyclotec mill (Tecator, Herndon, VA, USA) to pass through a 1 mm screen 5 and stored for qualitative analyses.…”