Kazutsuka Sanmiya

Mitochondrial small heat-shock protein enhances thermotolerance in tobacco plants

To clarify the role of mitochondrial small heat‐shock protein (MT‐sHSP) in the heat‐shock response, we introduced the tomato (Lycopersicon esculentum) MT‐sHSP gene under the control of the 35S promoter into tobacco (Nicotiana tabacum), and examined the thermotolerance of the transformed plants. Irrespective of the orientation, sense or antisense, of the gene, the transgenic plants exhibited a normal morphology and growth rate in the vegetative growth stage. When 4‐week‐old seedlings were exposed to sudden heat stress, the sense plants which overexpress the MT‐sHSP gene exhibited thermotolerance, whereas the antisense plants in which the expression of the gene is suppressed exhibited susceptibility.

Cloning of a cDNA that encodes farnesyl diphosphate synthase and the blue-light-induced expression of the corresponding gene in the leaves of rice plants☆

A cDNA encoding farnesyl diphosphate synthase (FPPS), a key enzyme in isoprenoid biosynthesis, was isolated from a cDNA library constructed from mRNA that had been prepared from etiolated rice (Oriza sativa L. variety Nipponbare) seedlings after three hours of illumination by a subtraction method. The putative polypeptide deduced from the 1289 bp nucleotide sequence consisted of 353 amino acids and had a molecular mass of 40 676 Da. The predicted amino acid sequence exhibited high homology to those of FPPS from Arabidopsis (73% to type 1, 72% to type 2) and white lupin (74%). Southern blot analysis showed that the rice genome might contain only one gene for FPPS. The highest level of expression of the gene was demonstrated in leaves by RNA blot analysis. Moreover, light, in particular blue light, effectively enhanced expression of the gene.

A novel importin α from rice, a component involved in the process of nuclear protein transport1

In eukaryotes, nuclear proteins that are transported into nuclei have nuclear localization signals (NLSs), which are recognized by proteins called importin α. We isolated a rice cDNA, #61L, and the corresponding gene that encodes a protein, which shows significant homology to the importin α. Although the encoded protein had only 23–27% amino acid identity to the importin αs from various organisms including plants, the fusion protein with glutathione S‐transferase showed a specific binding activity to the NLS of SV40 T‐antigen. These results suggest that the rice #61L protein is a novel importin α in plants.

Ovule-specific expression of the genes for mitochondrial and endoplasmic reticulum localized small heat-shock proteins in tomato flower

Tomato (Lycopersicon esculentum Mill.) mitochondrial small heat-shock protein (MT-sHSP) gene is known to respond quickly to heat stress in the leaves. To elucidate the role of sHSPs under heat stress in the reproductive organs and developing fruits, we examined the expression of the gene for MT-sHSP. In addition, the expression profiles of the genes for the cytosolic (class I and II) and endoplasmic reticulum (ER) localized small heat-shock proteins (class I-, class II- and ER-sHSP, respectively) were also examined. Although the examined genes were not or weakly expressed at a normal growth temperature, they all significantly responded to heat stress. In the flower, MT- and ER-sHSP were accumulated not in the pollen, but in the ovule. The expression profile suggests a role for sHSPs in protection against heat stress.