SHORTROOT-Mediated Intercellular Signals Coordinate Phloem Development in Arabidopsis Roots

Area of Science:

• Plant biology
• Developmental biology
• Molecular genetics

Background:

• Asymmetric cell division (ACD) and positional signals are crucial for plant tissue patterning.
• Arabidopsis root meristem phloem development involves ACDs for companion cells (CCs) and sieve elements (SEs), but their coordination is unclear.

Purpose of the Study:

• To elucidate the coordinated molecular mechanisms regulating phloem development in Arabidopsis roots.
• To investigate the role of the SHORTROOT (SHR) transcription factor in coordinating ACDs for distinct phloem cell types.

Main Methods:

• Analysis of SHR transcription factor movement and function in Arabidopsis root development.
• Investigated gene activation pathways involving microRNA165/6, NAC-REGULATED SEED MORPHOLOGY 1 (NARS1), and SECONDARY WALL-ASSOCIATED NAC DOMAIN PROTEIN 2 (SND2).
• Studied the positive feedforward loop between SHR, NARS1, and SND2 in phloem development.

Main Results:

• SHR movement into the endodermis activates microRNA165/6, regulating CC formation ACD.
• SHR movement into the phloem sequentially activates NARS1 and SND2, forming a positive feedforward loop for SE formation ACD.
• NARS1, produced in CCs, signals to the meristem to drive SE formation ACD, with SND2 amplifying this signal.

Conclusions:

• A novel regulatory mechanism coordinated by SHR governs Arabidopsis root phloem development.
• This mechanism involves distinct SHR actions in the endodermis and phloem, coupled with a feedforward loop involving NARS1 and SND2.
• The findings expand understanding of sophisticated vascular tissue patterning during postembryonic root growth.