Arabidopsis thaliana NGATHA1 transcription factor induces ABA biosynthesis by activating NCED3 gene during dehydration stress

Abstract

The plant hormone abscisic acid (ABA) is accumulated after drought stress and plays critical roles in the responses to drought stress in plants, such as gene regulation, stomatal closure, seed maturation, and dormancy. Although previous reports revealed detailed molecular roles of ABA in stress responses, the factors that contribute to the drought-stress responses—in particular, regulation of ABA accumulation—remain unclear. The enzyme NINE-CIS-EPOXYCAROTENOID DIOXYGENASE 3 (NCED3) is essential for ABA biosynthesis during drought stress, and the NCED3 gene is highly induced by drought stress. In the present study, we isolated NGATHAs (NGAs) as candidate transcriptional regulators of NCED3 through a screen of a plant library harboring the transcription factors fused to a chimeric repressor domain, SRDX. The NGA proteins were directly bound to a cis-element NGA-binding element (NBE) in the 5′ untranslated region (5′ UTR) of the NCED3 promoter and were suggested to be transcriptional activators of NCED3. Among the single-knockout mutants of four NGA family genes, we found that the NGATHA1 (NGA1) knockout mutant was drought-stress-sensitive with a decreased expression level of NCED3 during dehydration stress. These results suggested that NGA1 essentially functions as a transcriptional activator of NCED3 among the NGA family proteins. Moreover, the NGA1 protein was degraded under nonstressed conditions, and dehydration stress enhanced the accumulation of NGA1 proteins, even in ABA-deficient mutant plants, indicating that there should be ABA-independent posttranslational regulations. These findings emphasize the regulatory mechanisms of ABA biosynthesis during early drought stress.

Abscisic acid dynamics, signaling, and functions in plants

“…The flowering repressor SHORT VEGETATIVE PHASE (SVP), a central regulator of ABA catabolism, is able to decrease expression of CYP707A1/3 while enhancing expression of AtBG1 simultaneously in response to water deficits (Wang et al 2018c). Also, NGATHA proteins (NGAs) upregulate the expression of NCED3 via direct binding to its promoter (Sato et al 2018). The HD‐ZIP transcription factor HAT1, a negative regulator in ABA biosynthesis, which suppresses the expression of both ABA3 and NCED3 , can be phosphorylated and inactivated by SnRK2.3 (Tan et al 2018).…”

Seed germination and dormancy: The classic story, new puzzles, and evolution

“…Nodule Inception (NIN)‐like protein 8 (NLP8) has been identified as a direct inducer of CYP707A2 in imbibed seeds in response to nitrate and dormancy release (Yan et al ; summarized in Nonogaki ). On the other hand, direct upstream regulators of NCED that are responsible for the maintenance of dormancy in imbibed seeds are still missing, although the transcription factor (NGATHA1) involved in NCED3 induction during drought responses has been recently identified (Sato et al ). The intriguing story of NCED3 regulation in leaves by the root‐derived CLAVATA3/EMBRYO‐SURROUNDING REGIONRELATED 25 (CLE25) peptide has been revealed (Takahashi et al ).…”

Expression of a NGATHA1 Gene from Medicago truncatula Delays Flowering Time and Enhances Stress Tolerance

“…This result may indicate that MtNGA1 plays a role distinct from other B3 family transcription factors from M. truncatula. positively regulates abscisic acid (ABA) accumulation during dehydration stress due to the NCED3 gene, which encodes a key ABA biosynthetic enzyme [25].…”

“…Overexpression of NGAL2 significantly decreased seed size compared to that of the wild-type plants by restricting cell proliferation in the integuments of ovules and developing seeds, while NGAL3 overexpression increased size, although NGAL2 and NGAL3 act in the same pathway with the seed size regulator KLUH (KLU) to regulate seed growth [24]. In Arabidopsis, NGA1 activates the NCED3 gene by an NGA-binding element (NBE) in the 5 untranslated region (5 UTR) of the NCED3 promoter, and then positively regulates abscisic acid (ABA) accumulation during dehydration stress due to the NCED3 gene, which encodes a key ABA biosynthetic enzyme [25].In summary, NGA proteins affect plant organ development and regulate hormone synthesis and transport and drought-stress tolerance pathways. Many of the functions of NGA proteins have been Int.…”