Unravelling the molecular mechanism underlying drought stress tolerance in Dinanath (Pennisetum pedicellatum Trin.) grass via integrated transcriptomic and metabolomic analyses.

Dinanath grass (Pennisetum pedicellatum Trin.) is an extensively grown forage grass known for its significant drought resilience. In order to comprehensively grasp the adaptive mechanism of Dinanath grass in response to water deficient conditions, transcriptomic and metabolomics were applied in the leaves of Dinanath grass exposed to two distinct drought intensities (48-hour and 96-hour). Transcriptomic analysis of Dinanath grass leaves revealed that a total of 218 and 704 genes were differentially expressed under 48- and 96-hour drought conditions, respectively. The genes that were expressed differently (DEGs) and the metabolites that accumulated in response to 48-hour drought stress mainly showed enrichment in the biosynthesis of secondary metabolites, particularly phenolics and flavonoids. Conversely, under 96-hour drought conditions, the enriched pathways predominantly involved lipid metabolism, specifically sterol lipids. In particular, phenylpropanoid pathway and brassinosteroid signaling played a crucial role in drought response to 48- and 96-hour water deficit conditions, respectively. This variation in drought response indicates that the adaptation mechanism in Dinanath grass is highly dependent on the intensity of drought stress. In addition, different genes associated with phenylpropanoid and fatty acid biosynthesis, as well as signal transduction pathways namely phenylalanine ammonia-lyase, putrescine hydroxycinnamoyl transferase, abscisic acid 8'-hydroxylase 2, syntaxin-61, lipoxygenase 5, calcium-dependent protein kinase and phospholipase D alpha one, positively regulated with drought tolerance. Combined transcriptomic and metabolomic analyses highlights the outstanding involvement of regulatory pathways related to secondary cell wall thickening and lignin biosynthesis in imparting drought tolerance to Dinanath grass leaves. These findings collectively contribute to an enhanced understanding of candidate genes and key metabolites relevant to drought response in Dinanath grass. Furthermore, they establish a groundwork for the creation of a transcriptome database aimed at developing abiotic stress-tolerant grasses and major crop varieties through both transgenic and genome editing approaches.

Expression analysis of ß-carotene hydroxylase1 and opaque2 genes governing accumulation of provitamin-A, lysine and tryptophan during kernel development in biofortified sweet corn.

Traditional sweet corn possesses low levels of provitamin-A (proA), lysine and tryptophan. Mutant version of ß-carotene hydroxylase1 (crtRB1) gene affecting the accumulation of ß-carotene (BC), ß-cryptoxanthin (BCX) and proA, and opaque2 (o2) gene governing the enhancement of lysine and tryptophan were introgressed together into elite sweet corn inbreds through marker-assisted selection. Here, we analyzed the expression pattern of crtRB1 and o2 genes among introgressed and traditional sweet corn inbreds at 20-, 24- and 28-days after pollination (DAP). The introgressed inbreds possessed two- to sevenfolds higher BC, BCX, proA, lysine and tryptophan compared to their original inbreds. However, all the nutrients attained the peak at 20-DAP (BC: 9.95 µg/g, BCX: 8.21 µg/g, proA: 14.05 µg/g, lysine: 0.301%, tryptophan: 0.074%), which gradually reduced through 24-DAP (BC: 8.24 µg/g, BCX: 7.53 µg/g, proA: 12.01 µg/g, lysine: 0.273%, tryptophan: 0.057%) and 28-DAP (BC: 5.84 µg/g, BCX: 5.82 µg/g, proA: 8.75 µg/g, lysine: 0.202%, tryptophan: 0.037%). Biofortified sweet corn inbreds possessed significantly lower expression levels of crtRB1 (4.1-fold) and o2 (2.2-fold) compared to their wild type alleles in traditional sweet corn inbreds across DAPs. The expression of crtRB1 and o2 increased from 20-DAP to attain the highest peak at 24-DAP, and further decreased by 28-DAP. The transcript levels of crtRB1 were negatively correlated with BC (r = - 0.83), BCX (r = - 0.79) and proA (r = - 0.83) across dates of harvest. Lysine (r = - 0.83) and tryptophan (r = - 0.73) were also inversely associated with o2 transcript levels. This is the first report on expression of crtRB1 and o2 genes during kernel development in biofortified sweet corn. This information holds immense promise in understanding the dynamics of gene-regulation during kernel development in sweet corn.

Development of multinutrient-rich biofortified sweet corn hybrids through genomics-assisted selection of shrunken2, opaque2, lcyE and crtRB1 genes.

Sweet corn has gained worldwide popularity. Traditional sweet corn possesses low concentration of essential nutrients such as lysine (0.15-0.25%), tryptophan (0.03-0.04%) and provitamin-A (proA 3-4 ppm), and deficiency leads to serious health problems in humans. Here, stacking of shrunken2 (sh2), opaque2 (o2), lycopene epsilon cyclase (lcyE) and ß-carotene hydroxylase (crtRB1) genes  were undertaken in the parents of four hybrids viz., APQH1, APHQ4, APHQ5 and APHQ7 using marker-assisted backcross breeding (MABB). Gene-linked markers (umc2276 and umc1320) for sh2, while gene-based markers for o2 (umc1066 and phi057), lcyE (5'TE-InDel) and crtRB1 (3'TE-InDel), were used for genotyping in BC1F1, BC2F1 and BC2F2. Selected backcross progenies showed high recovery of recurrent parent genome (92.4-97.7%). The reconstituted sweet corn hybrids possessed significantly high lysine (0.390%), tryptophan (0.082%) and proA (21.14 ppm), coupled with high kernel sweetness (brix 18.96%). The improved sweet corn hybrids had high cob yield (12.22-15.33 t/ha) across three environments. These newly developed biofortified sweet corn hybrids possess great significance in providing balanced nutrition. This is the first report of combining sh2, o2, lcyE and crtRB1 genes for enrichment of sweet corn hybrids with multiple essential nutrients.