The SHORT-ROOT regulatory network in the endodermis development of Arabidopsis roots and shoots

The pair of GRAS transcription factors SHORTROOT (SHR) and SCARECROW (SCR) plays key roles in radial patterning of the Arabidopsis ( Arabidopsis thaliana ) root ground tissue. Recently, another GRAS transcription factor, SCARECROW-LIKE 23 (SCL23), the close homolog of SCR, has been shown to form heterodimeric complexes with its upstream regulator SHR. In turn, the SHR-SCL23 heterodimers bind to the SCL23 promoter, resulting in activation of SCL23 expression, which is reminiscent of the relationship between SHR and SCR. In addition, genetic analyses revealed that any mutant combination with shr displayed phenotypes nearly identical to those of shr in both root and shoot. Thus, it is likely that SHR acts as a master regulator in the SHR-SCR-SCL23 regulatory module. Intriguingly, SCL23 is able to modulate the activity/function of SHR in the hypocotyl by reducing both SHR mRNA accumulation and SHR protein movement, which forms a negative feedback loop in the SHR-SCR-SCL23 regulatory network. Taken together, through diverse approaches, recent studies have shown that the SHR-SCR-SCL23 module plays key roles in the development of the endodermis and its equivalent tissues (bundle sheath and starch sheath) in both roots and shoots.