Stepwise evolution of supercomplex formation with photosystem I is required for stabilization of chloroplast NADH dehydrogenase‐like complex: Lhca5‐dependent supercomplex formation in Physcomitrella patens

Abstract

In angiosperms, such as Arabidopsis and barley, the chloroplast NADH dehydrogenase-like (NDH) complex associates with two copies of photosystem I (PSI) supercomplex to form an NDH-PSI supercomplex for the stabilization of the NDH complex. Two linker proteins, Lhca5 and Lhca6, are members of the light-harvesting complex I (LHCI) family and mediate this supercomplex formation. The liverwort Marchantia polymorpha has branched from the basal land plant lineage and has neither Lhca5 nor Lhca6. Consequently, the NDH complex does not form a supercomplex with PSI in this plant. The Lhca6 gene does not seem to exist also in the moss Physcomitrella patens (Physcomitrella). Conversely, the Lhca5 gene has been found in Physcomitrella, although experimental evidence is still lacking for its contribution to NDH-PSI supercomplex formation as a linker. Here, we biochemically characterized the Lhca5 knock-out mutant (lhca5) in Physcomitrella. The NDH-PSI supercomplex observed in wild-type Physcomitrella was absent in the lhca5 mutant. Lhca5 protein was detected in this NDH-PSI supercomplex. Some PSI and NDH subunits were co-immunoprecipitated with Lhca5-HA. These results indicate that the Physcomitrella gene is the functional ortholog of Lhca5 reported in Arabidopsis. Between Physcomitrella and Arabidopsis, the stromal loop region is highly conserved in Lhca5 proteins but not in other LHCI members. We found that Lhca5 contributed to the stable accumulation of the NDH complex, but part of the NDH complex was still sensitive to high light intensity, even in the wild-type. We considered that angiosperms acquired another linker protein, Lhca6, to further stabilize the NDH complex.

Evolution of an assembly factor-based subunit contributed to a novel NDH-PSI supercomplex formation in chloroplasts

“…4a and Supplementary Tables 1 and 2 ), suggesting that PnsB1, PnsB4, and PnsB5 exist in both bryophytes. Consistent with this result, Physcomitrella mutants with the Pp3c16_3930V3 gene knocked out lacked NDH activity, suggesting that the gene encodes the NDH subunit PnsB4 in Physcomitrella 28 . The PnsB1 protein was also detected using the antibody against Arabidopsis PnsB1 in Marchantia and Physcomitrella 20 , 28 (Fig.…”

“…One of the linker proteins, Lhca6, was also acquired in angiosperms after branching from the bryophyte lineage 28 , as was PnsB2. SubB is the contact site for Lhca6 32 .…”

“…Lhca6 was likely acquired in a common ancestor of angiosperms, whereas Lhca5 is also conserved in the moss Physcomitrella patens (Physcomitrella) 28 . The Lhca6-dependent supercomplex formation was acquired relatively recently in the evolutionary history of angiosperms.…”

Structural basis for electron transport mechanism of complex I-like photosynthetic NAD(P)H dehydrogenase

“…9). The CEF activity was monitored by measuring the postillumination increase in chlorophyll fluorescence, a method extensively used in previous reports 31,32,[51][52][53][54] . Our results showed that NDH-1L exhibits the highest activity in mediating the CEF at pH 8.0 and pH 7.0, while at pH 6.0, its activity drastically decreased ( Supplementary Fig.…”

Role of cyclic and pseudo‐cyclic electron transport in response to dynamic light changes in Physcomitrella patens

“…On the contrary, overreduced PSI is instead prone to light damage to Fe‐S clusters present on the stromal side of the protein complex (Sonoike, Terashima, Iwaki, & Itoh, ; Tiwari et al, ). To avoid this phenomenon, other mechanisms capable of accepting electron from PSI are still present and likely active in flva pgrl1 KO plants (e.g., NDH‐dependent cyclic electron transport or the Mehler reaction, whose corresponding genes are present in P. patens genome; Alboresi et al, ; Kato, Odahara, Fukao, & Shikanai, ). The photorespiration pathway uses ATP and reducing power to regenerate ribulose‐1,5‐bisphosphate (RuBP) from 2‐phosphoglycolate, and it has also been demonstrated to represent a significant electron sink in bryophytes like mosses (Aro, Gerbaud, & André, ) or liverworts (Hanawa et al, ).…”