A mutation in THERMOSENSITIVE MALE STERILE 1, encoding a heat shock protein with DnaJ and PDI domains, leads to thermosensitive gametophytic male sterility in Arabidopsis

Abstract

SummaryIn most flowering plant species, pollination and fertilization occur during the hot summer, so plants must have evolved a mechanism that ensures normal growth of their pollen tubes at high temperatures. Despite its importance to plant reproduction, little is known about the molecular basis of thermotolerance in pollen tubes. Here we report the identification and characterization of a novel Arabidopsis gene, THERMOSENSITIVE MALE STERILE 1 (TMS1), which plays an important role in thermotolerance of pollen tubes. TMS1 encodes a Hsp40-homologous protein with a DnaJ domain and an a_ERdj5_C domain found in protein disulfide isomerases (PDI). Purified TMS1 expressed in Escherichia coli (BL21 DE3) had the reductive activity of PDI. TMS1 was expressed in pollen grains, pollen tubes and other vegetative tissues, including leaves, stems and roots. Heat shock treatment at 37°C increased its expression levels in growing pollen tubes as well as in vegetative tissues. A knockout mutation in TMS1 grown at 30°C had greatly retarded pollen tube growth in the transmitting tract, resulting in a significant reduction in male fertility. Our study suggests that TMS1 is required for thermotolerance of pollen tubes in Arabidopsis, possibly by functioning as a co-molecular chaperone.

Emerging features of ER resident J-proteins in plants

“…42 Despite lacking the CXXC sequence motif, Arabidopsis AtERdj3A protein expressed in Escherichia coli cells retains reductase activity in vitro. 8 AtERdj3A and OsERdj3A have other cysteines in their TRX domains, and it thus remains possible that plant ERdj3As may perform similar functions to mammalian ERdj5.…”

“…Arabidopsis AtERdj3A has a second TRX domain that is similar to the C-terminal redox inactive domain in mammalian P5 PDI, 8 but this region is not required for function and is not conserved between Arabidopsis and rice ERdj3A. 6,8 Since mammalian ERdj5 has four TRX domains at the C terminus, it is possible that plant ERdj3As could be orthologous to mammalian ERdj5. 16,17 Mammalian ERdj5 is involved in the reduction of BiP substrates and enhancement of their ability to be unfolded for retrotranslocation into cytoplasm.…”

“…Molecular cloning of the TMS1 gene revealed that it encodes AtERdj3A. 8 Although aterdj2a mutants also have defective pollen growth, 5 phenotypic differences are apparent between tsm1/aterdj3a and aterdj2a mutants. Pollen growth is severely reduced, even at normal temperature, in the aterdj2a mutant, which is therefore homozygous lethal.…”

“…The functions of most ERdjs in plants remain unclear; however, recent studies have revealed physiological roles for Arabidopsis ERdjs such as AtERdj2A, AtERdj3A and AtERdj3B. 5,7,8 In addition, rice OsERdj3A is localized in vacuoles under ER stress conditions, indicating that plant ERdjs display distinct characteristics from those in mammals. 6 This mini-review summarizes the current knowledge surrounding ERdjs in plants, as well as in mammals and yeast.…”

Functional analysis of Hsp70 superfamily proteins of rice (Oryza sativa)

“…Whereas DnaK system efficiently solubilized and refolded small protein aggregates (Diamant et al 2000), large protein aggregates are solubilized in concert with Hsp100/ ClpB (Diamant et al 2000;Acebron et al 2009). Expression of cytosolic Hsp70 genes is linked to acquired thermotolerance because of their property to reactivate the protein aggregates formed under various stress conditions (Lee and Schoffl 1996;Yang et al 2009;Qi et al 2011;Zhou et al 2012;Sung and Guy 2003). It is noted that Hsp70 may function as a negative feedback regulator of HSF activity (Shi et al 1998;Kim and Schoffl 2002).…”