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. 2012 Jul;63(12):4527-38.
doi: 10.1093/jxb/ers131. Epub 2012 May 21.

HPS4/SABRE regulates plant responses to phosphate starvation through antagonistic interaction with ethylene signalling

Hailan Yu  1 , Nan Luo, Lichao Sun, Dong Liu
Affiliations

HPS4/SABRE regulates plant responses to phosphate starvation through antagonistic interaction with ethylene signalling

Hailan Yu et al. J Exp Bot. 2012 Jul.

Abstract

The phytohormone ethylene plays important roles in regulating plant responses to phosphate (Pi) starvation. To date, however, no molecular components have been identified that interact with ethylene signalling in regulating such responses. In this work, an Arabidopsis mutant, hps4, was characterized that exhibits enhanced responses to Pi starvation, including increased inhibition of primary root growth, enhanced expression of Pi starvation-induced genes, and overproduction of root-associated acid phosphatases. Molecular cloning indicated that hps4 is a new allele of SABRE, which was previously identified as an important regulator of cell expansion in Arabidopsis. HPS4/SABRE antagonistically interacts with ethylene signalling to regulate plant responses to Pi starvation. Furthermore, it is shown that Pi-starved hps4 mutants accumulate more auxin in their root tips than the wild type, which may explain the increased inhibition of their primary root growth when grown under Pi deficiency.

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Figures

Fig. 1.
Fig. 1.
Growth characteristics, APase activities, and anthocyanin contents of the WT and the hps4 mutant. (A) Morphology of 9-day-old seedlings of the WT and hps4 grown on Pi-sufficient (P+) and Pi-deficient (P–) medium. (B) Detection of APase activity by BCIP staining on the root surfaces of WT and hps4 seedlings shown in A. (C) Root-associated APase activity in 9-day-old seedlings of the WT and hps4 grown on P+ and P– medium. (D) Anthocyanin contents in 12-day-old seedlings of the WT and hps4. For C and D, values represent the mean and SE of three replicates. Means with asterisks are significantly different from the WT (P < 0.05, two-sample t-test).
Fig. 2.
Fig. 2.
Analysis of PSI gene expression in the WT and the hps4 mutant. Four-day-old seedlings of the WT and hps4 grown on P+ or P– medium were used for real-time PCR analysis. The names of the genes examined are indicated on the top of each panel. Values are the means and SD of three biological replicates and represent fold changes normalized to transcript levels of the WT on P+ medium. Means with asterisks are significantly different from the WT (P < 0.05, two-sample t-test).
Fig. 3.
Fig. 3.
Molecular cloning of the HPS4 gene. (A) A diagram of the structure of the HPS4/SABRE protein. The AGI code of the HPS4 gene is indicated. The filled region indicates the segment that shares sequence homology with a group of Golgi-localized plant proteins. The positions of T-DNA insertions in the sab1-1mutant line and six SALK lines, and the position of the point mutation in hps4 are indicated. The changes in nucleotide and amino acid in the hps4 mutant are shown in parentheses. (B) Morphologies and BCIP staining of 9-day-old seedlings of the WT, hps4, sab1-1, and six SALK T-DNA insertion lines grown on P+ and P– medium. (C) Close-up view of BCIP staining of the seedlings shown in B.
Fig. 4.
Fig. 4.
Expression patterns of the HPS4 gene. (A) Relative expression of the HPS4 gene in different plant organs determined by q-PCR. (B) Tissue-specific expression patterns of the HPS4::GUS gene. Top row, from left to right: a 9-day-old seedling, a cotyledon, part of the root elongation zone, and root apex. Middle row, from left to right: a 20-day-old mature plant, stem, and a junction between leaf blade and leaf petiole. Bottom row, from left to right: a fully opened flower, petal, sepal, gynoecium, stamen, and silique.
Fig. 5.
Fig. 5.
Effects of the ethylene perception inhibitor Ag+ on root growth, APase activity, and anthocyanin accumulation of WT and hps4 seedlings. (A) Morphology of 9-day-old seedlings of WT and hps4 grown on P+ and P– medium with or without addition of 10 μM Ag+ (labels are provided below panel B). (B) Close-up view of APase activities detected by BCIP staining on the root surfaces of the seedlings shown in A. (C) Primary root length of 9-day-old seedlings of the WT and hps4 grown on P+ and P– medium with or without addition of 10 μM Ag+. (D) Anthocyanin accumulation in 9-day-old seedlings of the WT and hps4 grown on P– medium with or without addition of 10 μM Ag+. For C and D, values represent the mean and SE of three replicates. Means with asterisks are significantly different from the WT (P < 0.05, two-sample t-test).
Fig. 6.
Fig. 6.
IAA content, and expression of auxin-responsive genes and auxin biosynthetic genes between Pi-starved hps4 and Pi-starved WT. (A) Free IAA contents in apical 5 mm root sections of 9-day-old seedlings of Pi-starved hps4 and Pi-starved WT. (B) Relative expression of four auxin-responsive genes in the roots of 9-day-old Pi-starved hps4 and Pi-starved WT. (C) Relative expression of 10 auxin biosynthetic genes in the roots of 9-day-old Pi-starved hps4 and Pi-starved WT. In B and C, the expression of all the genes in the WT was set to 1. In A–C, values represent the mean and SE of three replicates. Means with asterisks are significantly different from the WT (P < 0.05, two-sample t-test).
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