Genetic analysis and identification of candidate genes for a narrow and long grain mutant (nlg1) in rice.

Grain size is one of the components that determine the rice yield. Exploring more key genes that regulating grain size and analyzing their molecular mechanisms are of great importance for precision breeding of rice. In this study, we screened a mutant nlg1(narrow and long grain 1) with narrow and long grains by mutagenizing the japonica rice variety ZH11 with EMS. Observation and statistical analysis of the outer surface of the mature glume of nlg1 by scanning electron microscopy revealed an increased number of longitudinal cells and a decreased number of transverse cells, along with a reduction in the width of transverse cells. These findings suggest that NLG1 may regulate grain size by simultaneously influencing the proliferation and expansion of lemma cells. The candidate gene was cloned by genome resequencing combined with MutMap analysis method. The results showed that the candidate gene of LOC_Os09g27590 was the previous reported gene, GS9, which encodes a protein with unknown domains. In the nlg1 mutant, a base C was inserted in the first exon of the candidate gene of LOC_Os09g27590, causing a frameshift mutation that leads to premature termination of protein translation. Further genetic complementation experiments showed that NLG1 rescued the phenotype of the nlg1 mutant. Therefore, this study identifies a novel GS9 allele mutation, and further dissection of its molecular regulatory networks in grain size control can provides a theoretical support and genetic resources for precise rice breeding.