Abstract
Carbohydrates (sugars) are an essential energy-source for all life forms. They take a significant share of our daily consumption and are used for biofuel production as well. However, sugarcane and sugar beet are the only two crop plants which are used to produce sugar in significant amounts. Here, we have discovered and fine-tuned a phenomenon in rice which leads them to produce sugary-grain. We knocked-out GCS1 genes in rice by using CRISPR technology, which led to fertilization failure and pollen tube-dependent ovule enlargement morphology (POEM) phenomenon. Apparently, the POEMed-like rice ovule (‘endosperm-focused’) can grow near-normal seed-size unlike earlier observations in Arabidopsis in which gcs1 ovules (‘embryo-focused’) were aborted quite early. The POEMed-like rice ovules contained 10–20% sugar, with extremely high sucrose content (98%). Trancriptomic analysis revealed that the osgcs1 ovules had downregulation of starch biosynthetic genes, which would otherwise have converted sucrose to starch. Overall, this study shows that pollen tube content release is sufficient to trigger sucrose unloading at rice ovules. However, successful fertilization is indispensable to trigger sucrose-starch conversion. These findings are expected to pave the way for developing novel sugar producing crops suited for diverse climatic regions.
Highlights
Carbohydrates are an essential energy-source for all life forms
Since Arabidopsis gcs[1] mutant showed clear pollen tube-dependent ovule enlargement morphology (POEM) phenomenon in earlier study[11], we first conducted a homology search to see whether O. sativa possessed GCS113 homologs or not
Pollinated rice styles were stained with aniline blue, which showed that osgcs[1] pollen tubes have germinated and grown along the style until reaching the female gametophyte, in a similar way to what happen with the Nipponbare pollen tubes
Summary
Carbohydrates (sugars) are an essential energy-source for all life forms. They take a significant share of our daily consumption and are used for biofuel production as well. 374 transcripts were up-regulated in both Nipponbare and osgcs[1] ovules indicating that PTC release itself is sufficient to trigger transcriptional changes in rice ovules (Fig. 2b, c and Supplementary Data 1, 2). As reported in Arabidopsis[11], multiple genes associated with cell expansion or cell division were significantly up-regulated in both Nipponbare and osgcs[1] ovules at 1DAP or later (Fig. 2d and Supplementary Data 3).
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