Generation of aroma in three-line hybrid rice through CRISPR/Cas9 editing of BETAINE ALDEHYDE DEHYDROGENASE2 (OsBADH2).

Aroma or fragrance in rice is a genetically controlled trait; Its high appreciation by consumers increases the rice market price. Previous studies have revealed that the rice aroma is controlled by a specific gene called BETAINE ALDEHYDE DEHYDROGENASE (OsBADH2), and mutation of this gene leads to the accumulation of an aromatic substance 2-acetyl-1-pyrroline (2-AP). The use of genetic engineering to produce aroma in commercial and cultivated hybrids is a contemporary need for molecular breeding. The current study reports the generation of aroma in the three-line hybrid restorer line Shu-Hui-313 (SH313). We created knock-out (KO) lines of OsBADH2 through the CRISPR/Cas9. The analysis of KO lines revealed a significantly increased content of 2AP in the grains compared with the control. However, other phenotypic traits (plant height, seed setting rate, and 1000-grain weight) were significantly decreased. These KO lines were crossed with a non-aromatic three-line hybrid rice male sterile line (Rong-7-A) to produce Rong-7-You-626 (R7Y626), R7Y627 and R7Y628. The measurement of 2-AP revealed significantly increased contents in these cross combinations. We compared the content of 2-AP in tissues at the booting stage. Data revealed that young spike stalk base contained the highest content of 2-AP and can be used for identification (by simple chewing) of aromatic lines under field conditions. In conclusion, our dataset offers a genetic source and illustrates the generation of aroma in non-aromatic hybrids, and outlines a straightforward identification under field conditions.

HCC1, a Polygalacturonase, Regulates Chlorophyll Degradation via the Ethylene Synthesis Pathway.

Chlorophyll degradation is an important physiological process and is essential for plant growth and development. However, how chlorophyll degradation is controlled at the cellular and molecular level remains largely elusive. Pectin is a main component of the primary cell wall, and polygalacturonases (PGs) is a group of pectin-hydrolases that cleaves the pectin backbone and release oligogalacturonide. Whether and how PGs affect chlorophyll degradation metabolism and its association with ethylene (ETH) have not been reported before. Here, we report a novel function of PG in a mutant 'high chlorophyll content1' hcc1, which displayed a decrease in growth and yield. Our morphological, biochemical and genetic analyses of hcc1, knockout lines and complementation lines confirm the function of HCC1 in chlorophyll degradation. In hcc1, the PG activity, ETH content and D-galacturonic acid (D-GA) was significantly decreased and showed an increase in the thickness of the cell wall. Exogenous application of ETH and D-GA can increase ETH content and induce the expression of HCC1, which further can successfully induce the chlorophyll degradation in hcc1. Together, our data demonstrated a novel function of HCC1 in chlorophyll degradation via the ETH pathway.