Identification of Putative RuBisCo Activase (TaRca1)—The Catalytic Chaperone Regulating Carbon Assimilatory Pathway in Wheat (Triticum aestivum) under the Heat Stress

Abstract

RuBisCo activase (Rca) is a catalytic chaperone involved in modulating the activity of RuBisCo (key enzyme of photosynthetic pathway). Here, we identified eight novel transcripts from wheat through data mining predicted to be Rca and cloned a transcript of 1.4 kb from cv. HD2985, named as TaRca1 (GenBank acc. no. KC776912). Single copy number of TaRca1 was observed in wheat genome. Expression analysis in diverse wheat genotypes (HD2985, Halna, PBW621, and HD2329) showed very high relative expression of TaRca1 in Halna under control and HS-treated, as compared to other cultivars at different stages of growth. TaRca1 protein was predicted to be chloroplast-localized with numerous potential phosphorylation sites. Northern blot analysis showed maximum accumulation of TaRca1 transcript in thermotolerant cv. during mealy-ripe stage, as compared to thermosusceptible. Decrease in the photosynthetic parameters was observed in all the cultivars, except PBW621 in response to HS. We observed significant increase in the Rca activity in all the cultivars under HS at different stages of growth. HS causes decrease in the RuBisCo activity; maximum reduction was observed during pollination stage in thermosusceptible cvs. as validated through immunoblotting. We observed uniform carbon distribution in different tissues of thermotolerant cvs., as compared to thermosusceptible. Similarly, tolerance level of leaf was observed maximum in Halna having high Rca activity under HS. A positive correlation was observed between the transcript and activity of TaRca1 in HS-treated Halna. Similarly, TaRca1 enzyme showed positive correlation with the activity of RuBisCo. There is, however, need to manipulate the thermal stability of TaRca1 enzyme through protein engineering for sustaining the photosynthetic rate under HS—a novel approach toward development of “climate-smart” crop.

Metabolic Reprogramming in Chloroplasts under Heat Stress in Plants

“…In wheat, northern blot analysis showed maximum accumulation of TaRCA1 transcript in thermotolerant cv. during mealy-ripe stage, as compared to thermosusceptible ones [ 170 ]. To test the hypothesis that thermostable RCA can improve photosynthesis under elevated temperatures, gene shuffling technology was used to generate several Arabidopsis thaliana RCA1 (short isoform) variants exhibiting improved thermostability [ 171 ].…”

A Conserved Sequence from Heat-Adapted Species Improves Rubisco Activase Thermostability in Wheat

“…Furthermore, the protein profile of wheat Rca determined by westernblot analysis shows that there are two bands corresponding to an aand a b-isoform and abundance of a third band in close proximity to the position of the original b-isoform when wheat is exposed to heat stress (Law and Crafts-Brandner, 2001;Ristic et al, 2009). It is unknown if the two Rca isoforms with similar molecular mass during heat stress relate to the TaRca1-b and TaRca2-b isoforms, although it is likely, as induction of the TaRca1-b gene in response to heat stress has been observed in certain cultivars of wheat (Kumar et al, 2016).…”

Terminal heat tolerance in wheat: An overview

“…The RuBisCo enzyme is deactivated by heat stress and the deactivity of RuBisCo has been observed within 7 days of imposed heat shock treatment (Kumar et al, 2016). Staygreen has also been studied extensively in different crops.…”