Expression of multiple expansin genes is associated with cell expansion in potato organs

Expansin proteins can induce the extension of isolated cell walls and are proposed to mediate the cell wall loosening that leads to cell expansion. Nine α-expansin cDNAs were isolated from potato (Solanum tuberosum), and their expression was examined in developing tubers and in rapidly growing etiolated stems. EXPA1 mRNA accumulated to high abundance in young expanding tubers, and in etiolated stems high EXPA1 mRNA accumulation in growing apical regions and low accumulation in basal non-growing regions was correlated with growth rate. The mRNAs of EXPA7 and EXPA8 also accumulated at relatively high levels in young expanding tubers, but not in elongating stems. Auxin treatment of excised stem segments rapidly increased cell elongation, and the mRNAs of EXPA1, EXPA3, EXPA4 and EXPA5 increased within 1 h. Growth rate under auxin treatment remained high for at least 7 h, and the mRNA abundance of EXPA1, EXPA4 and EXPA5 remained above that of the control during this time. The data show that multiple α-expansin genes are expressed in expanding cells of potato tuber and stem tissues, and expression of at least some of these genes is hormonally regulated during growth.