Serpin genes AtSRP2 and AtSRP3 are required for normal growth sensitivity to a DNA alkylating agent in Arabidopsis.
BACKGROUND
The complex responses of plants to DNA damage are incompletely understood and the role of members of the serpin protein family has not been investigated. Serpins are functionally diverse but structurally conserved proteins found in all three domains of life. In animals, most serpins have regulatory functions through potent, irreversible inhibition of specific serine or cysteine proteinases via a unique suicide-substrate mechanism. Plant serpins are also potent proteinase inhibitors, but their physiological roles are largely unknown.


RESULTS
Six Arabidopsis genes encoding full-length serpins were differentially expressed in developing seedlings and mature tissues. Basal levels of AtSRP2 (At2g14540) and AtSRP3 (At1g64030) transcripts were highest in reproductive tissues. AtSRP2 was induced 5-fold and AtSRP3 100-fold after exposure of seedlings to low concentrations of methyl methanesulfonate (MMS), a model alkylating reagent that causes DNA damage. Homozygous T-DNA insertion mutants atsrp2 and atsrp3 exhibited no differential growth when mutant and wild-type plants were left untreated or exposed to gamma-radiation or ultraviolet light. In contrast, atsrp2 and atsrp3 plants exhibited greater root length, leaf number and overall size than wild-type plants when exposed to MMS. Neither of the two serpins was required for meiosis. GFP-AtSRP2 was localized to the nucleus, whereas GFP-AtSRP3 was cytosolic, suggesting that they target different proteinases. Induction of cell cycle- and DNA damage-related genes AtBRCA1, AtBARD1, AtRAD51, AtCYCB1;1 and AtCYCD1;1, but not AtATM, was reduced relative to wild-type in atsrp2 and atsrp3 mutants exposed to MMS.


CONCLUSIONS
Expression of specific serpin genes (AtSRP2 and AtSRP3 in Arabidopsis) is required for normal responses of plants following exposure to alkylating genotoxins such as MMS.
Department of Chemistry and Biomolecular Sciences, Macquarie University, North Ryde, NSW 2109, Australia. joon-woo.ahn@students.mq.edu.au
Joon-Woo
JW
Ahn
Brian J
BJ
Atwell
Thomas H
TH
Roberts
D000477:Alkylating Agents / Q000494:pharmacology*; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D004249:DNA Damage; D004269:DNA, Bacterial; D005720:Gamma Rays; D018506:Gene Expression Regulation, Plant; D055786:Gene Knockout Techniques; D017343:Genes, Plant; D008741:Methyl Methanesulfonate / Q000494:pharmacology; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D018749:RNA, Plant / Q000235:genetics; D016415:Sequence Alignment; D015843:Serpins / Q000235:genetics / Q000378:metabolism*; D014466:Ultraviolet Rays
D000477:Alkylating Agents; D029681:Arabidopsis Proteins; D004269:DNA, Bacterial; D018749:RNA, Plant; D015843:Serpins; C036483:T-DNA; D008741:Methyl Methanesulfonate