Heat‐induced changes in the abundance of wheat Rubisco activase isoforms

Abstract

The Triticum aestivum (wheat) genome encodes three isoforms of Rubisco activase (Rca) differing in thermostability, which could be exploited to improve the resilience of this crop to global warming. We hypothesized that elevated temperatures would cause an increase in the relative abundance of heat-stable Rca1b. Wheat plants were grown at 25°C : 18°C (day : night) and exposed to heat stress (38°C : 22°C) for up to 5 d at pre-anthesis. Carbon (C) assimilation, Rubisco activity, CA1Pase activity, transcripts of Rca1b, Rca2b, and Rca2a, and the quantities of the corresponding protein products were measured during and after heat stress. The transcript of Rca1b increased 40-fold in 4 h at elevated temperatures and returned to the original level after 4 h upon return of plants to control temperatures. Rca1b comprised up to 2% of the total Rca protein in unstressed leaves but increased threefold in leaves exposed to elevated temperatures for 5 d and remained high at 4 h after heat stress. These results show that elevated temperatures cause rapid changes in Rca gene expression and adaptive changes in Rca isoform abundance. The improved understanding of the regulation of C assimilation under heat stress will inform efforts to improve wheat productivity and climate resilience.

The relative abundance of wheat Rubisco activase isoforms is post-transcriptionally regulated

“…The expression of the wheat Rca isoforms TaRca2-α and TaRca2-β , encoded by the highly expressed TaRca2 gene, increased during the first half of the photoperiod, with a peak at 8–10 h after the start of the 16 h photoperiod. The expression of TaRca1-β isoform was extremely low, in agreement with previous reports (Scafaro et al 2019a ; Degen et al 2021 ), and remained low throughout the entire diel cycle (Fig. 1 ).…”

“…In Arabidopsis , Camelina and spinach, equal amounts of Rca-α and Rca-β are present, while rice and soybean accumulate much more Rca-β than Rca-α (Salvucci et al 1987 ; Fukayama et al 2012 ; Chao et al 2014 ; Scafaro et al 2016 ). Similarly, in wheat, TaRca-β is much more abundant than TaRca-α (Law and Crafts-Brandner 2001 ; Degen et al 2021 ), and the Rca-α/β ratio remained constant during the whole diel cycle (12.5%, Fig. S3).…”

“…Of note is that the primers used were specific to the TaRbcS genes in chromosome 5 (group S3). As described by Degen et al ( 2021 ), TaRbcS genes can be grouped according to their sequence similarity, with gene groups S1 and S2 in chromosome 2 and group S3 in chromosome 5. In the same study, the abundance of TaRbcS2 and TaRbcS3 transcripts was comparable and higher than TaRbcS1 in wheat leaves that were sampled only at 4 h after the start of a 16 h photoperiod.…”

“…For qRT-PCR a 1:10 dilution of cDNA was used with SYBRGreen (Platinum® SYBR® Green qPCR SuperMix-UDG w/ROX, Life Technologies, UK), in 25 μL reactions, as per the manufacturer’s instructions. Primer pairs specific to TaRca1-β , TaRca2-β , TaRca2-α , TarbcL and TaRbcS (primers were specific for TaRbcS located on chromosome 5A, 5B and 5D, group S3 as described by Degen et al 2021 ), were used for qRT-PCR, alongside primers for two reference genes (Table S1). Primers were designed to bind to all three wheat sub-genomes, except for rbcL , which is encoded in the chloroplast genome.…”

“…Despite the characterisation of Rca isoforms in wheat (Carmo-Silva et al 2015 ; Perdomo et al 2019 ) and gene expression studies under abiotic stresses such as drought and temperature (Zhao et al 2017 ; Scafaro et al 2019a ; Degen et al 2021 ) little is known about diurnal regulation of their abundance. The three wheat Rca activate Rubisco at different rates and differ in their sensitivity to light stimuli, changes in the ADP/ATP ratio (Perdomo et al 2019 ).…”