Gibberellin regulates UV-B-induced hypocotyl growth inhibition in Arabidopsis thaliana

Figures & data

Table 1. Primer sequence for the real-time PCR

AGI No.	Gene	Primers (5ʹ→3ʹ)
At3G18780	Actin 2		GCTCTTCAGGAGCAATACGAAG GTTGGGATGAACCAGAAGGA
At5G51810	GA20ox2		TCCAACGATAATAGTGGCT TTGGCATGGAGGATAATGA
At4G25420	GA20ox1		TATCGAACGATAGATACAAGAGC TATCTTCTTGATGTGATGCTGTC
At1G15550	GA3ox1		CCATTCACCTCCCACACTCT GCCAGTGATGGTGAAACCTT
At1G78440	GA2ox1		CGGTTCGGGTCCACTATTTC ACCTCCCATTTGTCATCACCTG
At5G50915	bHLH-137		ACATTCACGTTCGAGC CGGAGCCAAAGTCATAG
At5G41315	GL3		CAATCTCAACGACTCCTCCAAGG AATGCCTGGACGGACGTTTG
At5g18800	RGA		CAAGGTTATCGTGTGGAGGAGAG CAAGCGGAGGTGGTAATGAGTG
At5g12250	GAI		CTATGCTCACCGACCTTAATCCT TGGTTAGACGAAGAAGCCGAAT
At4g20890	RGL1		ATCGGTTCACGGAATCGCTACAT ACATCACTCGGTCTTGGCTTGG
At3g62250	RGL2		CCGTGGTGCTCGTTGACTCT TTCTCCTGGTGAATCGCCTCAG
At5g11260	RGL3		AGCAATAGTAACAGCAACAAGAGGA GATAAGCACCACGGAACGAGT

Figure 1. UV-B exposure inhibits Arabidopsis hypocotyl elongation. The uvr8, rga-24, hy5, bbx24, wild type (Col), and wild type (Ler) seedlings were grown under white light for 4 d and subsequently exposed to UV-B radiation for 3 d

(a) Phenotype of hypocotyl elongation of wild type (Col-0), stoand hy5 mutant. (b–c). Hypocotyl length of uvr8, rga-24, hy5, sto, wild type (Col), and wild-type (Ler) seedlings grown in the presence or absence of UV-B radiation. The hypocotyl length was measured using ImageJ software. Different lowercase letters indicate statistically significant differences between seedlings grown in the presence or absence of UV-B radiation (Tukey’s test; P < 0.05).

Figure 2. GA₃ partly restores the hypocotyl growth of Col seedlings under UV-B light

(a). Wild-type (Col) seedlings grown under white light for 4 d and exposed to UV-B radiation for 3 d (scale bar = 1 mm); (b). The bar graph shows the hypocotyl length measured by ImageJ software. (c). The ratio (+UV-B)/(-UV-B) of hypocotyl length. Data are presented as mean ± standard error (n = 3; each replicate had at least 12 seedlings). Different lowercase letters indicate statistically significant differences between seedlings grown in the presence or absence of UV-B radiation (Tukey’s test; P < 0.05).

Figure 3. UV-B influences the expression of GA metabolic genes via UVR8. Wild type (Col) and uvr8-2 seedlings were grown in white light for 7 days and exposed to ±UV-B for 4 h

(a). GA₃ content in Arabidopsis seedlings; (b–d). mRNA levels of GA metabolism-related genes (GA20ox2, GA3ox1, and GA2ox1) quantified by real-time PCR. Error bars represent the standard error (SE) of the mean of three biological replicates. ‘**’ indicates statistically significant differences at P < 0.01; ‘NS’ indicates no significant difference.

Figure 4. UV-B affects the expression of DELLA-responsive genes via HY5. Arabidopsis seedlings were grown in white light for 7 d and exposed to ±UV-B for 4 h

(a–b). Relative expression levels of GL3 and bHLH-137 genes in wild type, hy5, and bbx24 mutants detected by real-time PCR. Error bars represent the standard error (SE) of the mean of three biological replicates. Different lowercase letters indicate statistically significant differences in gene expression levels (Tukey’s test; P < 0.05).

Figure 5. HY5 promotes RGA accumulation under UV-B irradiation. Seedlings were grown in white light for 7 d and exposed to ±UV-B for 4 h

(a–c). mRNA levels of GA metabolism-related genes (GA20ox1, GA3ox1, and GA2ox1) in wild type (WT) and hy5 mutant were quantified by real-time PCR; (d). RGA protein levels in WT, bbx24, rga-24, and hy5-215 after UV-B treatment; and (e). Gray value of RGA protein band (a). Error bars represent the standard error (SE) of the mean of three biological replicates. Different lowercase letters indicate statistically significant differences between the gene expression levels (Tukey’s test; P < 0.05).

Figure 6. Transcript levels of DELLA genes in wild-type WT and hy5-215 mutant quantified by qRT-PCR

Seedlings were grown in white light for 7 d and exposed to ±UV-B for 4 h. Relative expression levels of (a) GAI gene; (B) RGL3 gene; (c) RGA gene; (d) RGL1 gene; and (e) RGL2 gene. Error bars represent the standard error (SE) of the mean of three biological replicates. Different lowercase letters indicate statistically significant differences between the gene transcript levels (Tukey’s test; P < 0.05).

Figure 7. Model for GA involvement in UV-B-induced inhibition of hypocotyl elongation in Arabidopsis.

UV-B exposure causes UVR8 to bind with COP1 and regulates the transcription of the downstream gene HY5, promoting the accumulation of RGA protein (one of the most important member of DELLA family), reducing GA3 content, and ultimately inhibiting hypocotyl elongation. BBX24 negatively regulates the expression of HY5. Modified from Hayes.⁴⁷

Abbreviations

GA	gibberellin
GA3	Gibberelic acid
UVR8	UV RESISTANCE LOCUS 8
GAs	Exogenous gibberellins
COP1	CONSTITUTIVELY PHOTOMORPHOGENIC 1
HY5	ELONGATED HYPOCOTYL 5
RUP1/2	REPRESSOR OF UV-B PHOTOMORPHOGENESIS 1/2
GA20ox1	gibberellin 20-oxidase 1
bHLH-137	Basic helix-loop-helix-137
GL3	GLABRA3
GA20ox2	Gibberellin 20-oxidase 2
GA2ox1	Gibberellin 2-oxidase 1
GA3ox1	Gibberellin 3-oxidase 1
PIFs	PHYTOCHROME INTERACTING FACTORS
BBX24/STO	B-Box ZINC FINGER PROTEIN24/SALT TOLERANCE
GID1	GA-INSENSIVE DWARF1
LIP1–LONG1	orthologs of COP1–HY5 in Arabidopsis

Hayes S, Velanis CN, Jenkins GI, Franklin KA. UV-B detected by the UVR8 photoreceptor antagonizes auxin signaling and plant shade avoidance. Proc Natl Acad Sci U S A. 2014;111(32):11894–11899. doi:https://doi.org/10.1073/pnas.1403052111.

 PubMed Web of Science ®Google Scholar