Identification and gene mapping of yellow-leaf less-tillering mutant yllt1 in rice (Oryza sativa L.)

The phenotypes and genetic control of rice (Oryza sativa L.) mutant yllt1 (yellow leaf and less tillering 1) were analyzed. Results showed that chlorophyll a and chlorophyll b contents in yllt1 were 77.78% and 60.00% that of wild-type ‘T98B’, and abnormal chloroplasts with a few functional thylakoid lamellar were present at the seedling stage. At the vigorous tillering stage, tiller number in yllt1 was 21.43% that of the wild-type. Genetic analysis revealed that the recombination rate between the yellow leaf trait and less tillering trait was 0.00%, based on a F₂ population from yllt1 crossed with ‘T98B’, indicating that the two traits were both controlled by yllt1. Moreover, yllt1 was recessively inherited via a nuclear gene. We fine mapped yllt1 to Chromosome 11 using linkage analysis, and the LOC_Os11g05552 mutant, as verified by sequencing, was identified as a likely candidate for yllt1. It encoded a signal recognition particle 54 kD protein, chloroplast precursor (cpSRP54). In yllt1, deletion of cds. 29 (C) on exon 1 of cpSRP54 would damage the protein structure from the N-terminus to C-terminus. Based on quantitative real-time polymerase chain reaction (qRT-PCR), genes involved in chlorophyll synthesis, including OsCAO1, OsCAO2, and OsNOL, were significantly down-regulated in yllt1. Furthermore, the positive regulator of tillering (OsTAC1) was decreased by 50%, whereas the negative regulators (OsTB1 and OsDLT) were increased 4.5-fold compared with the wild-type. The results herein suggest that cpSRP54 is involved in the regulation of leaf color and tillering. In addition, our results should help to explore the intrinsic relationship between leaf color and tillering dependent on yllt1.