Ectopic expression of AtMYB115 and AtMYB118 induces green tissue formation in non-green organs of Arabidopsis thaliana.

Background: A dominant mutant, green root-dominant (grt-D), which exhibits a green-root phenotype, was identified using the GAL4-UAS activation tagging system in the Q2610 enhancer trap line of Arabidopsis thaliana (Arabidopsis).

Objective: To identify the gene responsible for the grt-D phenotype and investigate whether its ectopic expression induces green petal formation.

Methods: The gene responsible for the grt-D phenotype was identified via thermal asymmetric interlaced-polymerase chain reaction (PCR). The cloned gene and its homolog were expressed under the control of the Q2610 enhancer for root tip expression and the APETALA3 (AP3) or PISTILLATA (PI) promoter for petal-preferential expression.

Results: The 5 × UAS tag in grt-D was located 111 base pairs upstream of the start codon of AtMYB115. Ectopic expression of AtMYB115 or its closest homolog, AtMYB118, under the Q2610 enhancer recapitulated the grt-D green-root phenotype, indicating functional equivalence between the two genes. To examine their effect on petal development, AtMYB115 and AtMYB118 were expressed under the AP3 and PI promoters. The resulting transgenic lines (AP3 >  > AtMYB115, AP3 >  > AtMYB118, PI >  > AtMYB115, and PI >  > AtMYB118) developed short, pale green petals and sterile stamens. The green petals exhibited reduced expression of STAY-GREEN 1, which encodes Mg-dechelatase, a key enzyme involved in chlorophyll degradation, suggesting that the green-petal phenotype results from impaired chlorophyll breakdown.

Conclusion: These findings demonstrate that the ectopic expression of AtMYB115 and AtMYB118 induces green tissue development in non-green organs of Arabidopsis.