HIGH-TILLERING AND DWARF 12 regulates photosynthesis and plant architecture by affecting carotenoid biosynthesis in rice.

Photosynthesis and plant architecture are important factors influencing grain yield in rice (Oryza sativa L.). Here, we identified the high-tillering and dwarf 12 (htd12) mutant and analyzed the effects of the HTD12 mutation on these important factors. HTD12 encodes a 15-cis-ζ-carotene isomerase (Z-ISO) belonging to the NnrU protein family, as revealed by positional mapping and transformation experiments. Sequence analysis showed that a single nucleotide transition from guanine (G) to adenine (A) in the 3' acceptor site between the 1 st intron and 2 nd exon of HTD12 alters its mRNA splicing in htd12 plants, resulting in a 49-amino acid deletion that affects carotenoid biosynthesis and photosynthesis in this mutant. In addition, compared to the wild type, htd12 had significantly lower levels of ent-2'-epi-5-deoxystrigol (epi-5DS), a native strigolactone (SL), in both roots and root exudates, resulting in an obvious increase in tiller number and decrease in plant height. These findings indicate that HTD12, the rice homolog of Z-ISO, regulates chloroplast development and photosynthesis by functioning in carotenoid biosynthesis and modulates plant architecture by affecting SL levels.