Analysis of the Rac/Rop small GTPase family in rice: expression, subcellular localization and role in disease resistance.
Plant-specific Rac/Rop small GTPases function as molecular switches for numerous signal transduction events, including defense responses. To understand the function of each of the seven Rac/Rop family members in rice, we studied the tissue-specific expression patterns of Rac/Rop genes by semi-quantitative reverse transcription-PCR (RT-PCR), and also Rac/Rop subcellular localization using green fluorescent protein (GFP) fusion proteins in transient expression systems. We also investigated the roles of these genes in disease resistance by testing single Rac/Rop-RNAi (RNA interference) plants against the rice blast pathogen Magnaporthe grisea. Our studies show that expression of OsRac2, 6 and 7 is very low in leaf blades, and reveal a strong correlation between the number of lysine and/or arginine (KR) residues in the polybasic region of Rac/Rop GTPases and their subcellular distribution in vivo. Infection assays showed that OsRac1 is a positive regulator of blast resistance, confirming previous observations, whereas OsRac4 and OsRac5 are negative regulators of blast resistance. OsRac6 may make minor contributions to disease resistance, while OsRac3 and OsRac7 are probably not involved in defense. Therefore, our study suggests that the rice Rac/Rop family plays multiple roles in diverse cellular activities and has both positive and negative functions in disease resistance.
Chen
Letian
L
Laboratory of Plant Molecular Genetics, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, 630-0192 Japan.
Shiotani
Kenji
K
Togashi
Takashi
T
Miki
Daisuke
D
Aoyama
Misa
M
Wong
Hann Ling
HL
Kawasaki
Tsutomu
T
Shimamoto
Ko
K
D000595:Amino Acid Sequence; D018506:Gene Expression Regulation, Plant / Q000235:genetics / Q000502:physiology; D007113:Immunity, Innate / Q000235:genetics / Q000502:physiology; D020082:Magnaporthe / Q000472:pathogenicity; D008969:Molecular Sequence Data; D020559:Monomeric GTP-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D012275:Oryza / Q000201:enzymology* / Q000235:genetics / Q000382:microbiology*; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D011523:Protoplasts / Q000378:metabolism; D034622:RNA Interference; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid
D010940:Plant Proteins; D020559:Monomeric GTP-Binding Proteins