The SAUR41 subfamily of SMALL AUXIN UP RNA genes is abscisic acid inducible to modulate cell expansion and salt tolerance in Arabidopsis thaliana seedlings

Abstract

Background and Aims Most primary auxin response genes are classified into three families: AUX/IAA, GH3 and SAUR genes. Few studies have been conducted on Arabidopsis thaliana SAUR genes, possibly due to genetic redundancy among different subfamily members. Data mining on arabidopsis transcriptional profiles indicates that the SAUR41 subfamily members of SMALL AUXIN UP RNA genes are, strikingly, induced by an inhibitory phytohormone, abscisic acid (ABA). We aimed to reveal the physiological roles of arabidopsis SAUR41 subfamily genes containing SAUR40, SAUR41, SAUR71 and SAUR72. Methods Transcriptional responses of arabidopsis SAUR41 genes to phytohormones were determined by quantitative real-time PCR. Knock out of SAUR41 genes was carried out with the CRISPR/Cas9 (clustered regulatory interspaced short palindromic repeats/CRISPR-associated protein 9) genome editing technique. The saur41/40/71/72 quadruple mutants, SAUR41 overexpression lines and the wild type were subjected to ultrastructural observation, transcriptome analysis and physiological characterization. Key Results Transcription of arabidopsis SAUR41 subfamily genes is activated by ABA but not by gibberellic acids and brassinosteroids. Quadruple mutations in saur41/40/71/72 led to reduced cell expansion/elongation in cotyledons and hypocotyls, opposite to the overexpression of SAUR41; however, an irregular arrangement of cell size and shape was observed in both cases. The quadruple mutants had increased transcription of calcium homeostasis/signalling genes in seedling shoots, and the SAUR41 overexpression lines had decreased transcription of iron homeostasis genes in roots and increased ABA biosynthesis in shoots. Notably, both the quadruple mutants and the SAUR41 overexpression lines were hypersensitive to salt stress during seedling establishment, whereas specific expression of SAUR41 under the ABA-responsive RD29A (Responsive to Desiccation 29A) promoter in the quadruple mutants rescued the inhibitory effect of salt stress. Conclusions The SAUR41 subfamily genes of arabidopsis are ABA inducible to modulate cell expansion, ion homeostasis and salt tolerance. Our work may provide new candidate genes for improvement of plant abiotic stress tolerance.

The SAUR41 subfamily of cell expansion-promoting genes modulates abscisic acid sensitivity and root touch response: a possible connection to ion homeostasis regulation

“…Thus, we generated saur41/40/71/72 quadruple mutants using the CRISPR/Cas9 (Clustered Regulatory Interspaced Short Palindromic Repeats/CRISPR Associated Protein 9) genome editing technique. 5 As expected, by a quantitative real-time PCR analysis, we found that the Arabidopsis SAUR41 subfamily genes were activated by ABA but not by gibberellic acids (GA) and BR. 5 Here, the ABA sensitivity of the three genotypes, the saur41/40/71/72 quadruple mutants, the SAUR41 overexpression lines (OE-SAUR41), and the wild-type (Col-0), was tested by sowing the seeds of same age on low concentrations (0-0.75 μM) of exogenous ABA.…”

“…5 As expected, by a quantitative real-time PCR analysis, we found that the Arabidopsis SAUR41 subfamily genes were activated by ABA but not by gibberellic acids (GA) and BR. 5 Here, the ABA sensitivity of the three genotypes, the saur41/40/71/72 quadruple mutants, the SAUR41 overexpression lines (OE-SAUR41), and the wild-type (Col-0), was tested by sowing the seeds of same age on low concentrations (0-0.75 μM) of exogenous ABA. The ABA concentrations used here were unable to block Arabidopsis seed germination, but reduced the cotyledon greening/expansion rate in a dose-dependent manner.…”

“…3,4 Our recent work on the functional characterization of a SAUR (SMALL AXUIN UP RNA) subfamily of Arabidopsis genes supported this notion. 5 Proteins encoded by primary auxin response genes are generally classified into three families, namely AUX/IAAs (AUXIN/ INDOLE-3-ACETIC ACIDs), GH3 (GRETCHEN HAGEN3s), and SAURs. 6 Aux/IAAs are transcription repressors for the nuclear auxin signaling processes, GH3s are acyl acid amido synthetases that catalyze the conjugation of indole acetic acid (IAA), jasmonic acid (JAS), or salicylic acid (SA) with amino acids, 7 while the nature of SAURs remains largely unknown.…”

“…14 Results showed that the cotyledon greening/expansion rates of the quadruple mutants declined sharply with the increased ABA dose compared with the wild-type ( Figure 1). Conversely, the overexpression lines showed some resistance to the ABA treatment ( Figure 1); although, they contained a higher concentration of endogenous ABA, 5 indicating that the accelerated seedling establishment induced by ectopic SAUR41s is epistatic to the potential inhibitory effects of exogenous ABA. Transcriptionally, the quadruple mutants altered the expression of certain transcription factors related to ABA signaling (GBF3, TEM1, and RAV1), while the SAUR41 overexpression altered the expression of the genes encoding an ABA receptor PYL1 and an ABA co-receptor HAI1.…”

pH-dependent transcriptional profile changes in iron-deficient Arabidopsis roots

“…Also, several genes involved in cell wall organization such as the pectin lyase At2g43890, the pectin methylesterase ATPM EI11 and the expansin EXP17 showed a large high pH /low pH ratio, possibly to compensate compromised cell expansion at alkaline pH. This supposition is supported by a large high pH/low pH ratio of the auxin-related genes SAUR41 and SAUR72, which have been associated with the regulation of cell expansion [13,18]. High pH /low pH ratios below one were observed for STRESS INDUCED FACTOR1 (SIF1), a root-specific, membraneanchored LRR kinase with undefined function [33], the aluminum-activated malate transporter ALMT1, and the Cys2-His2 zinc-finger domain transcription factor SEN-SITIVE TO PROTON RHIZOTOXICITY 2 (STOP2).…”