Monogalactosyl Diacylglycerol Synthase 3 (OsMGD3) affects phosphate utilization and acquisition in rice

Galactolipids are essential for compensating for the loss of phospholipids by "membrane lipid remodeling" in plants under phosphorus (P) deficiency. Monogalactosyl diacylglycerol (MGDG) synthases catalyze the synthesis of MGDG which is further converted into digalactosyl diacylglycerol (DGDG), later replacing phospholipids in the extraplastidial membranes. However, the roles of these enzymes are not well explored in rice. In this study, the rice MGDG synthase gene, OsMGD3 was identified and functionally characterized. We showed that plant phosphate (Pi) status and transcription factor OsPHR2 are involved in the transcriptional regulation of OsMGD3. CRISPR/Cas9 knockout (KO) and overexpression (OE) lines of OsMGD3 were generated to explore its potential role in rice adaptation to Pi deficiency. Compared to WT, OsMGD3 KO lines displayed a reduction while OE lines showed an enhanced, Pi acquisition and utilization. Further, OsMGD3 showed a predominant role in roots, altering lateral root growth. Our comprehensive lipidomic analysis revealed the role of OsMGD3 in membrane lipid remodeling in addition to a role in regulating diacylglycerol and phosphatidic acid levels that affected the expression of Pi transporters. Our study highlights the role of OsMGD3 in affecting both internal P utilization and P acquisition in rice

Brassica juncea Lines with Substituted Chimeric GFP-CENH3 Give Haploid and Aneuploid Progenies on Crossing with Other Lines

Haploids and doubled haploids are invaluable for basic genetic studies and in crop improvement. A novel method of haploid induction through genetic engineering of the Centromere Histone Protein gene, CENH3, has been demonstrated in Arabidopsis. The present study was undertaken to develop haploid inducer (HI) lines of Brassica juncea based on the principles elaborated in Arabidopsis. B. juncea was found to carry three copies of CENH3 which generated five different transcripts, of which three transcripts resulted from alternative splicing. Unlike Arabidopsis thaliana where native CENH3 gene was knocked out for constructing HI lines, we used RNAi approach to knockdown the native CENH3 genes. Further, to rescue CENH3 silenced cells, a GFP-CENH3-tailswap construct having N terminal GFP fused to H3.3 tail sequences and synthetic CENH3 histone fold domain sequences was devised. A total 38 transgenic B. juncea plants were regenerated following co-transformation with both silencing and rescue cassettes and transgenics carrying either or both the constructs were obtained. Transgenic status was confirmed through PCR, Southern and qRT-PCR analyses. Co-transformed lines were crossed to untransformed B. juncea or a line expressing only GFP-tailswap. FACS and cytological analyses of progenies revealed partial or complete elimination of B. juncea chromosomes thereby giving rise to aneuploids and haploid. This is the first report in a polyploid crop demonstrating that CENH3 engineering could be used to develop HI lines