Arginine decarboxylase (polyamine synthesis) mutants of Arabidopsis thaliana exhibit altered root growth

Abstract

SummaryPutrescine and polyamines are produced by two alternative pathways in plants. One pathway starts with the enzyme arginine decarboxylase; the other with ornithine decarboxylase. The authors developed an in vivo screening strategy to identify mutants with low levels of arginine decarboxylase activity. The screen requires both a primary screen of the M2 generation and a secondary screen of the M3 generation. The method used was to screen 15 000 EMS-mutagenized M2 seedlings for low levels of arginine decarboxylase (ADC) activity and identified seven mutants that fall into two complementation groups. These mutants have from 20% to 50% of wild-type enzyme activity. Morphological alterations common among the mutants include increased levels of lateral root branching. The authors obtained a double mutant combining the alleles with the lowest activities from the two complementation groups; this has lower ADC enzyme activity and putrescine levels than either of the single mutants. The double mutant has highly kinked roots that form a tight cluster; it also has narrower leaves, sepals, and petals than either single mutant or wild-type, and delayed flowering. These results suggest there may be more than one ADC gene in Arabidopsis, and that ADC and polyamine levels play roles in root meristem function and in lateral growth of leafhomolog organs.

BUD2, encoding an S-adenosylmethionine decarboxylase, is required for Arabidopsis growth and development

“…In higher plants, putrescine might be more related to root initiation [53], even though controversy exists [20,54]. Our findings that bud2 plants contain more putrescine and have the enhanced root growth appear to support the argument that putrescine has a promotive effect on root growth.…”

“…So far, two members of ADC, SPDS and SPMS genes [6,19,24,47], and four members of SAMDC genes have been identified in the Arabidopsis genome [29]. Previous studies indicated that ADC and SPDS members are functionally redundant, because a mutation in either gene member does not cause significant phenotypic changes [20,21,24,47]. Neverthe- less, the disruption of ACL5, one of SPMS genes, results in a severe dwarfism and an increased organ vascularization [11,22], indicating that two SPMS genes are not completely redundant during developmental process.…”

“…Although application of inhibitors is very useful in studying the polyamine biosynthetic pathway and in ex- [11,[19][20][21][22][23][24]. However, no mutant defective in SAMDC has been reported yet, although SAMDC cDNAs were cloned and their transgenic plants have been generated [25][26][27][28][29].…”

“…Putrescine is derived either from ornithine catalyzed by ornithine decarboxylase (ODC) or from arginine through several steps catalyzed by arginine decarboxylase (ADC), agmatine iminohydrolase and N-carbamoylputrescine amidohydrolase. Spermidine and spermine are synthesized from putrescine through spermidine and spermine synthases (SPDS and SPMS) from the donor of decarboxylated S-adenosylmethionine (dcSAM), which is produced from S-adenosylmethionine (SAM) by the action of S-adenosylmethionine decarboxylase (SAMDC).Although application of inhibitors is very useful in studying the polyamine biosynthetic pathway and in ex- [11,[19][20][21][22][23][24]. However, no mutant defective in SAMDC has been reported yet, although SAMDC cDNAs were cloned and their transgenic plants have been generated [25][26][27][28][29].…”

Polyamines: potent modulators of plant responses to stress

“…Mutants deficient in PA biosynthesis have been isolated from several biological systems. Watson et al (1998) isolated two EMS mutants of A. thaliana namely spe-1 and spe-2 which map to ADC2 that are reduced in ADC activity. Kasinathan and Wingler (2004) reported that the salt treatment that induced polyamine accumulation in wild-type plants did not lead to polyamine accumulation in spe1 and spe2 mutants.…”