Page 5 - S. Plant biology

Pathogenesis-Related Thaumatin-Like Genes are Involved in

the ABA Signal Transduction Pathway
Eun Joo Park and Tae-Houn Kim*
Department of Biotechnology/Convergence Science of Bio-Health, Duksung Women’s University, 01369, Seoul, Korea

Abstract

The sweet tasting protein thaumatin was first isolated from Thaumatococcus daniellii Benth and found in various plant species [1]. In Arabidopsis, twenty-two
thaumatin-like genes were identified, but specific functions of each genes need to be clarified [2]. The abiotic stress hormone ABA was previously reported to be
involved in the regulation of biotic stress signal transduction. Granting that biotic and abiotic stress signaling pathways might be tightly interconnected by sharing
certain components in both pathway, characterizations of such factors that exist in common will contribute to understanding the mechanism of signaling interaction.
Through characterization of quadruple and quintuple mutants of thaumatin-like genes, we found altered physiological phenotypes from the mutants under ABA
treatment. Moreover, ABA inductions of the ABA-responsive genes were also affected in the mutants which is consistent with the observed physiological phenotypes.
In addition to the biotic stress-related phenotypes in the mutants, ABA signaling-related phenotypes of the thaumatin mutant suggest that thaumatin-like genes may
have a role in the regulation of interactions between abiotic and biotic stress signaling pathways.

Result and Discussion
Among twenty-two thaumatin like gens, closely related five genes were selected based on sequence similarities, and the quadruple and quintuple
mutants were generated in order to investigate the function of thaumatin like gens under abiotic condition (Figure 1A and D).

A B C D

Figure 1. The quadruple and quintuple T-DNA mutants show altered ABA responses
A. PCR genotyping of the quadruple and quintuple mutants of thaumatin-like genes B. Six-day-old seedlings were transferred to growth media containing 40 μM ABA for qthau and 20 μM ABA for
quinthau) C. Four-week-old qthau/quinthau were treated with 30 μM ABA for 2 days, and proline level was quantified using 1.25% ninhydrin solution at 3 rd day D. Four-week-old qthau were under
drought condition for four weeks, and survived plants were counted at 5 th day after rehydration

The quadruple and quintuple mutants showed reduced
sensitivities to ABA treatments (Figure 1B, C and 2). The
recovery of ABA-induced proline synthesis in the quintuple
mutant indicates that the five selected thaumatin genes are
not simply redundant in certain functions (Figure 1C and 2)
Figure 2. The ABA-induced gene expression is affected in
qthau and quinthau
Ten-day-old qthau seedlings were treated with 30 μM ABA for 5 hours, and seven-day-
old quinthau seedlings were under 30 μM ABA for 3 hours

PstDC3000
qthau was infected either with PstDC3000 or PstDC300
AvrRpm1 in order to test whether thaumatin-like genes
were involved in the pathogen triggered immune
response (PTI) or the effector triggered immune response
(ETI). Enhanced bacterial growth was shown in qthau, and
this result further supported by reduced expression levels
PstDC3000 avrRPM1 of pathogenesis related genes (Figure 3).
Figure 3. The qthau mutant showed enhanced
susceptibility toward PstDC3000
Four-week-old leaves were infected with PstDC3000 or PstDC300 AvrRpm1,
and the bacterial growth were counted at third day after infection. Leaves excised
at 2 dpi (days post inoculation) were used for gene expression analyses.

References

1. van der Wel, H. and K. Loeve, Isolation and characterization of thaumatin I and II, the sweet-tasting proteins from Thaumatococcus daniellii Benth. Eur J Biochem, 1972. 31(2): p. 221-5.
2. Faillace, G.R., et al., Genome-wide analysis and evolution of plant thaumatin-like proteins: a focus on the origin and diversification of osmotins. Mol Genet Genomics, 2019. 294(5): p. 1137-
1157.