Colocalizations between several QTLs for cell wall degradability and composition in the F288 x F271 early maize RIL progeny raise the question of the nature of the possible underlying determinants and breeding targets for biofuel capacity
Résumé
Understanding the genetic basis of the different traits which contribute to a given value of cell wall degradability is a key issue towards the breeding of grasses with higher feeding value or higher capability for bioenergy production. A quantitative trait loci (QTL) investigation for cell wall degradability and several cell wall component traits including lignin content, p-hydroxycinnamic acid content, and lignin monomeric structure was thus done with a simultaneous search for underlying candidate genes in the F288 x F271 recombinant inbred line progeny. Genotype effects were highly significant for all cell wall investigated traits (P < 0.001) and much higher than genotype x environment interaction effects. Out of 42 QTLs mapped, 11 and 23 QTLs explained more than 20 and 15 % of the observed trait phenotypic variation, respectively. Twenty-three QTLs were gathered into four large clusters shown in bins 3.06, 4.09, 6.05, and 6.07. Colocalizations of cell wall degradability QTLs occurred with lignin content QTLs and lignin structure QTLs. Moreover, for two positions, there were also colocalizations with etherified ferulic acid QTLs. Such simultaneous colocalizations between QTLs for cell wall degradability and both lignin- and ferulate-related traits led to questioning the possible underlying genetic determinant(s). A cluster of (linked) genes involved in the different mechanisms of cell wall biosynthesis and/or assembly is likely the simplest situation to consider. However, a single "master" regulation factor located upstream in the pathway of cell wall biosynthesis and assembly cannot be definitely ruled out. Candidate genes putatively involved in cell wall degradability variations highlighted especially the presence of ZmMYB Hv5/EgMYB1-like and COV-like genes in any of the clusters. Moreover, besides potential regulatory candidates, there are a number of candidates of still unknown functions. The question of the nature of the possible QTL underlying determinants is still partly unanswered, even if the results obtained strongly suggested that, in this progeny, genes involved in monolignol biosynthesis and important Arabidopsis NAC are not likely candidates. In addition, the positions of candidate genes suggested that ghost QTL positions should also be considered.