Arabidopsis plants harbouring a mutation in AtSUC2, encoding the predominant sucrose/proton symporter necessary for efficient phloem transport, are able to complete their life cycle and produce viable seed.
OBJECTIVE
AtSUC2 encodes a sucrose/proton symporter that localizes throughout the collection and transport phloem and is necessary for efficient transport of sucrose from source to sink tissues in Arabidopsis thaliana. Plants harbouring homozygous AtSUC2 null alleles accumulate sugar, starch, and anthocyanin in mature leaves, have severely delayed development and stunted growth and, in previous studies, failed to complete their life cycle by producing viable seed.


METHODS
An AtSUC2 allele with a T-DNA insertion in the second intron was analysed. Full-length transcript from this allele is not produced, and a truncated protein translated from sequences upstream of the insertion site did not catalyse sucrose uptake into yeast, supporting the contention that this is a null allele. Mutant plants were grown in a growth chamber with a diurnal light/dark cycle, and growth patterns recorded.


RESULTS
This allele (SALK_038124, designated AtSUC2-4) has the hallmarks of previously described null alleles but, despite compromised carbon partitioning and growth, produces viable seeds. The onset of flowering was chronologically delayed but occurred at the same point in the plastochron index as wild type.


CONCLUSIONS
AtSUC2 is important for phloem loading and is therefore fundamental to phloem transport and plant productivity, but plants can complete their life cycle and produce viable seed in its absence. Arabidopsis appears to have mechanisms for mobilizing reduced carbon from the phloem into developing seeds independent of AtSUC2.
University of North Texas, Department of Biological Sciences, 1155 Union Circle #305220, Denton, TX 76203-5017, USA.
Avinash C
AC
Srivastava
Kasturi
K
Dasgupta
Eric
E
Ajieren
Gabriella
G
Costilla
Roisin C
RC
McGarry
Brian G
BG
Ayre
D017360:Arabidopsis / Q000235:genetics* / Q000254:growth & development* / Q000378:metabolism; D001692:Biological Transport; D050260:Carbohydrate Metabolism; D002482:Cellulose / Q000378:metabolism; D004269:DNA, Bacterial / Q000235:genetics; D026901:Membrane Transport Proteins / Q000235:genetics*; D016254:Mutagenesis, Insertional; D009154:Mutation / Q000235:genetics*; D052585:Phloem / Q000378:metabolism*; D019441:Plant Epidermis / Q000166:cytology / Q000378:metabolism; D018515:Plant Leaves / Q000166:cytology / Q000254:growth & development / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics*; D011522:Protons; D036226:Seedlings / Q000378:metabolism; D012639:Seeds / Q000254:growth & development*; D013213:Starch / Q000378:metabolism; D013395:Sucrose / Q000378:metabolism; D027981:Symporters / Q000235:genetics*
D004269:DNA, Bacterial; D026901:Membrane Transport Proteins; D010940:Plant Proteins; D011522:Protons; D027981:Symporters; C036483:T-DNA; C078729:sucrose transport protein, plant; D013395:Sucrose; D002482:Cellulose; D013213:Starch