Figure 7.

Model: SMB, ANAC087, and ANAC046 Control Different Aspects of Root Cap Cell Death.

In Arabidopsis, PCD is the final step of differentiation of both the columella and the LRC. In the columella (shown in yellow), ANAC087 and ANAC046 redundantly control the timing of PCD onset by regulating the expression of at least three PCD-associated genes: BFN1, EXI1, and RNS3. Furthermore, SMB is expressed in the columella (Bennett et al., 2010), and SMB was shown to function not only upstream of BFN1, EXI1, and RNS3, but also of some additional PCD-associated genes (Fendrych et al., 2014). In the LRC (shown in blue), so far only ANAC087 and SMB have been shown to be involved in PCD regulation. Again, both ANAC087 and SMB orchestrate the expression of BFN1, EXI1, and RNS3, whereas SMB has some additional PCD-associated targets (Fendrych et al., 2014). However, even though both ANAC087 and SMB are expressed in the entire LRC, it appears that PCD is differentially regulated at the distal part compared with the proximal zone.