AtMyb7, a subgroup 4 R2R3 Myb, negatively regulates ABA-induced inhibition of seed germination by blocking the expression of the bZIP transcription factor ABI5.

Various Myb proteins have been shown to play crucial roles in plants, including primary and secondary metabolism, determination of cell fate and identity, regulation of development and involvement in responses to biotic and abiotic stresses. The 126 R2R3 Myb proteins (with two Myb repeats) have been found in Arabidopsis; however, the functions of most of these proteins remain to be fully elucidated. In the present study, we characterized the function of AtMyb7 using molecular biological and genetic analyses. We used qRT-PCR to determine the levels of stress-response gene transcripts in wild-type and atmyb7 plants. We showed that Arabidopsis AtMyb7 plays a critical role in seed germination. Under abscisic acid (ABA) and high-salt stress conditions, atmyb7 plants showed a lower germination rate than did wild-type plants. Furthermore, AtMyb7 promoter:GUS seeds exhibited different expression patterns in response to variations in the seed imbibition period. AtMyb7 negatively controls the expression of the gene encoding bZIP transcription factor, ABI5, which is a key transcription factor in ABA signalling and serves as a crucial regulator of germination inhibition in Arabidopsis.

TTG1-mediated flavonols biosynthesis alleviates root growth inhibition in response to ABA.

KEY MESSAGE: Our results demonstrate that the flavonoids biosynthetic pathway can be effectively manipulated to confer enhanced plant root growth under water-stress conditions. Abscisic acid (ABA) is one of most important phytohormones. It functions in various processes during the plant lifecycle. Previous studies indicate that ABA has a negative effect on root growth and branching. Auxin is another key plant growth regulator that plays an essential role in plant growth and development. In contrast to ABA, auxin is a positive regulator of root growth and development at low concentrations. This study was performed to help understand whether flavonoids can suppress the effect of ABA on lateral root growth. The recessive TRANSPARENT TESTA GLABRA 1 (ttg1) mutant was characterized on ABA and sucrose treatments. It was determined that auxin mobilization could be altered by modifying flavonoids biosynthesis, which resulted in alterations of root architecture in response to ABA treatment. Moreover, transgenic TTG1-overexpression (TTG1-OX) seedlings exhibited enhanced root length and lateral root number compared to wild-type seedlings grown under normal or stress conditions. Genetic manipulation of the flavonoids biosynthetic pathway could therefore be employed successfully for the improvement of plant root systems by overcoming the inhibition of ABA and some abiotic stresses.