THE ARABIDOPSIS TRANSCRIPTION FACTOR ATHB22 IS INVOLVED IN GERMINATION AND PLANT GROWTH

TRIONFINI, V.; ATTALLAH C; CHAN, R.L.; WELCHEN, E.

Congreso; Reunión conjunta LXI SAIB - XV SAMIGE; 2020

SAIB - SAMIGE

AtHB22 (Arabidopsis thaliana Homeobox 22) is a transcription factor (TF) belonging to the HD-Zip I (Homeodomain-Leucine Zipper I) family of Arabidopsis thaliana. Members of this family have been broadly associated with developmental processes in response to different environmental factors. To understand the role of AtHB22, we obtained and studied by histochemistry transgenic plants carrying a segment of its promoter (pHB22) fused to the β-glucuronidase (GUS) reporter gene. GUS expression driven by the pHB22 promoter was discretely observed in the shoot apical meristem at 4, 8, and 12 days after sowing, at the edges of cotyledons, in rosette petioles, cauline leaf margins, axillary buds, sepal margins, and floral pedicels. No GUS expression was detected in root tissues or siliques in pHB22:GUS plants. Moreover, we characterized insertional athb22 mutant plants, analyzing the impact of lacking this protein at different stages of Arabidopsis development. The athb22 mutants exhibited significantly shorter roots in comparison to wild-type (WT) seedlings grown on in vitro MS medium-plates. The athb22 plants also exhibited a marked delay in germination and higher ABA-sensitivity compared to WT plants. Lack of AtHB22 also generates seedlings with longer hypocotyls than WT plants at the same age. No differences were detected in the leaf area neither in the number of leaves nor in the flower developmental transition time when plants were grown on soil under control conditions. Our results suggest that AtHB22 is a positive regulator of germination and could be involved in the plant response to the phytohormone ABA during this developmental stage. Moreover, AtHB22 acts as a positive regulator of root growth and could be involved in leaf morphogenesis. In this sense, the AtHB22 expression pattern described here is similar to that of its paralog AtHB51, which has been previously reported as essential for leaf morphogenesis and bract formation. Interestingly, AtHB51 was associated with the endoreduplication process in stipules. More efforts have to be done to deepen the role of AtHB22 in the development of Arabidopsis under normal growth conditions or during stressful situations, and its possible interaction with other members of the HD-Zip 1 family during these processes.