AIP1, Encoding the Small Subunit of Acetolactate Synthase, Is Partially Responsible for Resistance to Hypoxic Stress in Arabidopsis thaliana

Dongsu Choi,Geunmuk Im

doi:10.3390/plants10112251

Abstract

Flooding is a significant stress to land plants, depriving them of essential oxygen. Plants have evolved diverse strategies with variable success to survive flooding. Similar strategies have been described in organisms from other kingdoms. Several fungal species can successfully survive a low-oxygen environment by increasing their branched-chain amino acid (BCAA) contents. BCAAs may act as alternative electron acceptors in the respiratory chain under an oxygen-limited environment. The key and first enzyme for BCAA biosynthesis is acetolactate synthase (ALS). We identified two homologous genes encoding the small subunit of ALS in Arabidopsis (Arabidopsis thaliana). We determined that ALS INTERACTING PROTEIN1 (AIP1), which encodes the small subunit of ALS, is strongly expressed in all organs and highly expressed under submergence and low-oxygen stresses. We also showed that the overexpression of AIP1 confers tolerance to low-oxygen stress. These results indicate that ALS may play an essential role under prolonged flooding or oxygen deficiency in Arabidopsis.

Highlights

acetolactate synthase (ALS), is strongly expressed in all organs and highly expressed under submergence and low-oxygen stresses
We determined that ALS INTERACTING PROTEIN1 (AIP1), which encodes the small subunit of ALS, is strongly expressed in all organs and highly expressed under submergence and low-oxygen stresses
AIP1 showed a relatively higher expression level in leaves, while AIP3 was highly expressed in flowers, the expression patterns of these two genes were very similar (Figure 1A,B)

Summary

Organ-Specific Expression Patterns of AIP1 and AIP3 Genes

AIP1 and AIP3 genes were expressed in all organs tested. AIP1 showed a relatively higher expression level in leaves, while AIP3 was highly expressed in flowers, the expression patterns of these two genes were very similar (Figure 1A,B). AIP1 showed its strongest upregulation at 16 h after initiation of submergence, reaching levels ~2.5 times higher than air controls, before decreasing (Figure 2A). Assessment of the Tolerance to Hypoxia of AIP1-Overexpressing Lines by Recovery-Survival. Assessment of the Tolerance to Hypoxia of AIP1-Overexpressing Lines by Recovery-Survival Rates. To assess the contribution of AIP1 to tolerance against low-oxygen environments, we generated transgenic Arabidopsis lines overexpressing AIP1 (fused to GFP). To evaluate the tolerance of these transgenic plants to 16 h of hypoxic stress, we measured their survival rate following a 3-day recovery period. The GFP-AIP1-1-2 line significantly was significantly lower than that of the control Col-0 (Figure 4), in agreement with the higher survival score measured in the overexpression line (Figure 3).

Electrolyte fromconditions leaf disks between

Measurement of BCAA Contents in a GFP-AIP1-Overexpressing Line

Plant Materials and Growth Conditions

RNA Extraction and cDNA Synthesis

Tissue-Specific Expression of AIP1 and AIP3

Expression of AIP1 and AIP3 Genes upon Submergence and Hypoxia Conditions

Generation of AIP1-Overexpressing Arabidopsis Transformants

Assessment of Tolerance to Hypoxia by AIP1 Transformants Based on Electrolyte