Recessive waxy1 and opaque2 genes synergistically regulate accumulation of amylopectin, lysine and tryptophan in maize

Abstract

Traditional maize is poor in amylopectin (75%), lysine (0.200%), and tryptophan (0.045%). While the recessive waxy1 (wx1) gene enhances amylopectin and the recessive opaque2 (o2) gene increases lysine and tryptophan. Here, we analyzed transcripts of wx1 and o2 genes in (i) three wild-type (Wx1Wx1/O2O2), (ii) six waxy (wx1wx1/O2O2), (iii) four QPM (Wx1Wx1/o2o2), and (iv) eight waxy-QPM (wx1wx1/o2o2) inbreds at 20-, 30- and 40-days after pollination (DAP). The waxy inbreds possessed ∼1.4-fold higher amylopectin, while QPM inbreds showed 1.5- and 1.7-fold more accumulation of lysine and tryptophan over wild types. Interestingly, double mutant (wx1wx1/o2o2) had 2.1% higher amylopectin, and 15.6% and 16.6% more lysine and tryptophan, respectively over single mutants. Amylopectin showed an increase from 20-DAP (94.66%) to 30-DAP (96.56%) with a peak at 40-DAP (97.32%). On contrary, lysine and tryptophan peaked at 20-DAP (lysine: 0.552%, tryptophan: 0.267%), which gradually reduced through 30-DAP (lysine: 0.448%, tryptophan: 0.166%) and 40-DAP (lysine: 0.325%, tryptophan: 0.081%). Waxy and QPM inbreds possessed significantly lower expression of wx1 (∼3.0-fold) and o2 (∼1.1-fold) alleles over wild-type alleles (Wx1 and O2). Expression of wx1 and o2 in double mutant was 57.8% and 80.7% lower over single mutants, respectively. This is the first report on the expression of wx1 and o2 genes during maize kernel development.