DNAL7, a new allele of NAL11, has major pleiotropic effects on rice architecture

MAIN CONCLUSION

dnal7, a novel allelic variant of the OsHSP40, affects rice plant architecture and grain yield by coordinating auxins, cytokinins, and gibberellic acids. Plant height and leaf morphology are the most important traits of the ideal plant architecture (IPA), and discovering related genes is critical for breeding high-yield rice. Here, a dwarf and narrow leaf 7 (dnal7) mutant was identified from a γ-ray treated mutant population, which exhibits pleiotropic effects, including dwarfing, narrow leaves, small seeds, and low grain yield per plant compared to the wild type (WT). Histological analysis showed that the number of veins and the distance between adjacent small veins (SVs) were significantly reduced compared to the WT, indicating that DNAL7 controls leaf size by regulating the formation of veins. Map-based cloning and transgenic complementation revealed that DNAL7 is allelic to NAL11, which encodes OsHSP40, and the deletion of 2 codons in dnal7 destroyed the His-Pro-Asp (HPD) motif of OsHSP40. In addition, expression of DNAL7 in both WT and dnal7 gradually increased with the increase of temperature in the range of 27-31 °C. Heat stress significantly affected the seedling height and leaf width of the dnal7 mutant. A comparative transcriptome analysis of WT and dnal7 revealed that DNAL7 influenced multiple metabolic pathways, including plant hormone signal transduction, carbon metabolism, and biosynthesis of amino acids. Furthermore, the contents of the cytokinins in leaf blades were much higher in dnal7 than in the WT, whereas the contents of auxins were lower in dnal7. The contents of bioactive gibberellic acids (GAs) including GA1, GA3, and GA4 in shoots were decreased in dnal7. Thus, DNAL7 regulates rice plant architecture by coordinating the balance of auxins, cytokinins, and GAs. These results indicate that OsHSP40 is a pleiotropic gene, which plays an important role in improving rice yield and plant architecture.

Expression and function analysis of a rice OsHSP40 gene under salt stress

Heat shock proteins (HSPs) play essential roles in both plant growth and abiotic stress tolerance. In rice, OsHSP40 was recently reported to regulate programmed cell death (PCD) of suspension cells under high temperature. However, the expression and functions of OsHSP40 under normal growth or other abiotic stress conditions is still unknown. We reported the expression and function of a rice OsHSP40 gene under salt stress. Homologous proteins of OsHSP40 were collected from the NCBI database and constructed the neighbor-joining (NJ) phylogenetic tree. The expression pattern of OsHSP40 was detected by qRT-PCR under NaCl (150 mM) treatment. Then, identified a rice T-DNA insertion mutant oshsp40. At last, we compared and analyzed the phenotypes of oshsp40 and wild type under salt stress. OsHSP40 was a constitutively expressed small HSP (sHSP) gene and was close related to other plant sHSPs. Moreover, the expression of OsHSP40 was regulated by salt, varying across time points and tissues. Furthermore, the growth of T-DNA insertion mutant of OsHSP40 (designated as oshsp40) was suppressed by NaCl (150 mM) compared with that of the WT at seedling stage. Detailed measurement showed root and shoot length of the oshsp40 seedlings were significantly shorter than those of the WT seedlings under NaCl stress. In addition, the pot experiment results revealed that seedlings of oshsp40 withered more seriously compared with those of WT after NaCl treatment and recovery, and that survival rate and fresh weight of oshsp40 seedlings were significantly reduced. Taken together, these data suggested that OsHSP40 had multiple functions in rice normal growth and abiotic stress tolerance.