Isolation of cloned cDNAs to auxin-responsive poly(A) + RNAs of elongating soybean hypocotyl

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Abstract
Auxin-responsive c[complementary]DNA clones were isolated from a cDNA library prepared from elongating soybean hypocotyl poly(A)+RNA. The expression of 2 such sequences was assessed by RNA blot hybridization analyses during normal developmental transitions in the soybean hypocotyl and during incubation of sections excised from the region of cell elongation. The concentrations of these poly(A)+RNA are higher in the elongating zone than in the apical and mature zones of the hypocotyl. Both poly(A)+RNA are depleted during incubation of the sections in the absence of auxin. The loss of 1 of these sequences (pJCW1) is prevented by the addition of auxin to the incubation medium while the other sequence (pJCW2) increases above the initial level in the presence of auxin. The addition of auxin to auxin-depleted tissue in which the sequences are depleted, results in rapid accumulation of these poly(A)+RNA; pJCW1 accumulates to the control level while pJCW2 increases well above the control level. A highly selective effect of auxin occurs on the expression of a small number of mRNA in tissues undergoing cell elongation and cell division in response to auxin. Although the data are suggestive of a close association between auxin action and altered gene expression, a causal relationship was not established. It seems highly unlikely, however, that such specific effects of auxin on gene expression are unimportant in auxin physiology.