Brassinolides and IAA induce the transcription of four α-expansin genes related to development in Cicer arietinum

Four different cDNAs encoding α-expansins have been identified in Cicer arietinum (Ca-EXPA1, Ca-EXPA2, Ca-EXPA3 and Ca-EXPA4). The shared amino acid sequence similarity among the four α-expansin proteins ranged from 67 to 89%. All of them display common characteristics such as molecular mass (around 24 kDa), amino acid numbers, and also the presence of a signal peptide. The transcription pattern of chickpea α-expansin genes in seedlings and plants suggests a specific role for each of the four α-expansins in different phases of development or in different plant organs. High levels of Ca-EXPA2 transcripts coincide with maximum epicotyl and stem growth, indicating an important involvement of this particular α-expansin in elongating tissues. Ca-EXPA3 would be related to radicle development, while Ca-EXPA4 seems to be involved in pod development. A considerable increase in the level of all Ca-EXPA transcripts accompanied the indole acetic acid (IAA) plus brassinolide (BR)-induced elongation of excised epicotyl segments. This IAA + BR induction was seen even for the chickpea expansin genes whose transcription was not affected by IAA or BR alone.