ABSCISIC ACID INSENSITIVE 3 regulates abscisic acid‐responsive gene expression with the nuclear factor Y complex through the ACTT ‐core element in P hyscomitrella patens

The phytohormone ABA and the transcription factor ABSCISIC ACID INSENSITIVE 3 ( ABI 3)/ VIVIPAROUS 1 ( VP 1) function in protecting embryos during the desiccation stage of seed development. In a similar signaling pathway, vegetative tissue of the moss P hyscomitrella patens survives desiccation by activating downstream genes (e.g. LEA 1) in response to ABA and ABI 3. We show that the P p LEA 1 promoter responds to P p ABI 3 primarily through the ACTT ‐core element (5′‐ TCC ACTT GTC ‐3′), while the ACGT ‐core ABA ‐responsive element ( ABRE ) appears to respond to ABA alone. We also found by yeast‐two‐hybrid screening that P p ABI 3A interacts with P p NF ‐ YC 1, a subunit of CCAAT box binding factor ( CBF )/nuclear factor Y ( NF ‐Y). P p NF ‐ YC 1 increased the activation of the P p LEA 1 promoter when incubated with P p ABI 3 A , as did NF ‐ YB , NF ‐ YC , and ABI 3 from Arabidopsis. This new response element ( ACTT ) is responsible for activating the ABI 3‐dependent ABA response pathway cooperatively with the nuclear factor Y ( NF ‐ Y ) complex. These results further define the regulatory interactions at the transcriptional level for the expression of this network of genes required for drought/desiccation tolerance. This gene regulatory set is in large part conserved between vegetative tissue of bryophytes and seeds of angiosperms and will shed light on the evolution of this pathway in the green plant lineage.