ABCB1 and ABCB19 auxin transporters have synergistic effects on early and late Arabidopsis anther development

Arabidopsis abcbl abcb19 double mutants defective in the auxin transporters ABCB1/PGP1 and ABCB19/PGP19 are altered in stamen elongation, anther dehiscence and pollen maturation. To assess the contribution of these transporters to stamen development we performed phenotypic, histological analyses, and in situ hybridizations on abcbl and abcbl9 single mutant flowers. We found that pollen maturation and anther dehiscence are precocious in the abcbl but not in the abcb19 mutant. Accordingly, endothecium ligniflcation is altered only in abcbl anthers. Both abcbl and abcb1 abcb19 stamens also show altered early development, with asynchronous anther Iocules and a multilayer tapetum. DAPI staining showed that the timing of meiosis is asynchronous in abcbl abcb19 anther Iocules, while only a small percentage of pollen grains are non- viable according to Alexander＇s staining. In agreement, TAM （TARDY ASYNCHRONOUS MEIOSIS）, as well as BAM2 （BARELY ANY MERISTEM）involved in tapetal cell development--areoverexpressed in abcbl abcb19 young flower buds. Corre- spondingly, ABCB1 and ABCB19 mRNA localization supports the observed phenotypes of abcbl and abcbl abcb19 mutant anthers. In conclusion, we provide evidence that auxin transport plays a significant role both in early and late stamen development： ABCB1 plays a major role during anther development, while ABCB19 has a synergistic role.

Molecular bases of Sorcin-dependent resistance to chemotherapeutic agents

Soluble resistance-related calcium binding protein(Sorcin)is a protein initially labelled“resistance-related”,since it is co-amplified with ABCB1 in multidrug(MD)-resistant cells.While for years Sorcin overproduction was believed to be a by-product of the co-amplification of its gene with the P-glycoprotein gene,many recent studies view Sorcin as an oncoprotein,playing an important role in MD resistance(MDR).Sorcin is one of the most highly expressed calciumbinding proteins,which is overexpressed in many human tumors and MD resistant cancers,and represents a novel MDR marker.Sorcin expression in tumors inversely correlates with patients’response to chemotherapies and overall prognosis.Sorcin is highly expressed in MDR cell lines over their parent cells.Sorcin overexpression by gene transfection increases drug resistance to a variety of chemotherapeutic drugs in many cancer lines.On the other hand,Sorcin silencing leads to reversal of drug resistance in many cell lines.This review describes:(1)the roles of Sorcin in the cell;(2)the studies showing Sorcin overexpression in tumors and cancer cells;(3)the studies showing the effects of Sorcin overexpression and silencing;(4)the molecular effects of Sorcin overexpression;and(5)the structural and genetic bases of Sorcin-dependent MDR.