AUTHOR=Yang Sun Ui , Kim Hyojin , Kim Ryeo Jin , Kim Jungmook , Suh Mi Chung 

TITLE=AP2/DREB Transcription Factor RAP2.4 Activates Cuticular Wax Biosynthesis in Arabidopsis Leaves Under Drought

JOURNAL=Frontiers in Plant Science

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2020.00895

DOI=10.3389/fpls.2020.00895

ISSN=1664-462X

ABSTRACT=<p>Drought is a critical environmental stress that limits growth and development of plants and reduces crop productivity. The aerial part of land plants is covered with cuticular waxes to minimize water loss. To understand the regulatory mechanisms underlying cuticular wax biosynthesis in <italic>Arabidopsis</italic> under drought stress conditions, we characterized the role of an AP2/DREB type transcription factor, RAP2.4. <italic>RAP2.4</italic> expression was detected in one-week-old seedlings and rosette leaves, stems, stem epidermis, cauline leaves, buds, flowers, and siliques of 6-week-old <italic>Arabidopsis</italic>. The levels of <italic>RAP2.4</italic> transcripts increased with treatments of abscisic acid (ABA), mannitol, NaCl, and drought stress. Under drought, total wax loads decreased by approximately 11% and 10%, and in particular, the levels of alkanes, which are a major wax component, decreased by approximately 11% and 12% in <italic>rap2.4-1</italic> and <italic>rap2.4-2</italic> leaves, respectively, compared with wild type (WT) leaves. Moreover, the transcript levels of cuticular wax biosynthetic genes, <italic>KCS2</italic> and <italic>CER1</italic>, decreased by approximately 15–23% and 32–40% in <italic>rap2.4-1</italic> and <italic>rap2.4-2</italic> leaves, respectively, relative to WT 4 h after drought treatment, but increased by 2- to 12-fold and 3- to 70-fold, respectively, in three independent <italic>RAP2.4</italic> OX leaves relative to WT. Epicuticular wax crystals were observed on the leaves of <italic>RAP2.4</italic> OX plants, but not on the leaves of WT. Total wax loads increased by 1.5- to 3.3-fold in leaves of <italic>RAP2.4</italic> OX plants relative to WT. Cuticular transpiration and chlorophyll leaching occurred slowly in the leaves of <italic>RAP2.4</italic> OX plants relative to WT. Transcriptional activation assay in tobacco protoplasts showed that RAP2.4 activates the expression of <italic>KCS2</italic> and <italic>CER1</italic> through the involvement of the consensus CCGAC or GCC motifs present in the <italic>KCS2</italic> and <italic>CER1</italic> promoter regions. Overall, our results revealed that RAP2.4 is a transcription factor that activates cuticular wax biosynthesis in <italic>Arabidopsis</italic> leaves under drought stress conditions.</p>