Characterization of photosynthetic protein complexes in conchocelis and blades of Pyropia yezoensis (Rhodophyta)

Quantification of Photosynthetic Pigments in Neopyropia yezoensis Using Hyperspectral Imagery

Phycobilisomes and chlorophyll-a (Chla) play important roles in the photosynthetic physiology of red macroalgae and serve as the primary light-harvesting antennae and reaction center for photosystem II. Neopyropia is an economically important red macroalga widely cultivated in East Asian countries. The contents and ratios of 3 main phycobiliproteins and Chla are visible traits to evaluate its commercial quality. The traditional analytical methods used for measuring these components have several limitations. Therefore, a high-throughput, nondestructive, optical method based on hyperspectral imaging technology was developed for phenotyping the pigments phycoerythrin (PE), phycocyanin (PC), allophycocyanin (APC), and Chla in Neopyropia thalli in this study. The average spectra from the region of interest were collected at wavelengths ranging from 400 to 1000 nm using a hyperspectral camera. Following different preprocessing methods, 2 machine learning methods, partial least squares regression (PLSR) and support vector machine regression (SVR), were performed to establish the best prediction models for PE, PC, APC, and Chla contents. The prediction results showed that the PLSR model performed the best for PE (R _Test ² = 0.96, MAPE = 8.31%, RPD = 5.21) and the SVR model performed the best for PC (R _Test ² = 0.94, MAPE = 7.18%, RPD = 4.16) and APC (R _Test ² = 0.84, MAPE = 18.25%, RPD = 2.53). Two models (PLSR and SVR) performed almost the same for Chla (PLSR: R _Test ² = 0.92, MAPE = 12.77%, RPD = 3.61; SVR: R _Test ² = 0.93, MAPE = 13.51%, RPD =3.60). Further validation of the optimal models was performed using field-collected samples, and the result demonstrated satisfactory robustness and accuracy. The distribution of PE, PC, APC, and Chla contents within a thallus was visualized according to the optimal prediction models. The results showed that hyperspectral imaging technology was effective for fast, accurate, and noninvasive phenotyping of the PE, PC, APC, and Chla contents of Neopyropia in situ. This could benefit the efficiency of macroalgae breeding, phenomics research, and other related applications.

Co-suppression in Pyropia yezoensis (Rhodophyta) Reveals the Role of PyLHCI in Light Harvesting and Generation Switch

The red macroalga Pyropia yezoensis is an economically important seaweed widely cultured in Asian countries and is a model organism for molecular biological and commercial research. This species is unique in that it utilizes both phycobilisomes and transmembrane light-harvesting proteins as its antenna system. Here, one of the genes of P. yezoensis (PyLHCI) was selected for introduction into its genome to overexpress PyLHCI. However, the co-suppression phenomenon occurred. This is the first documentation of co-suppression in algae, in which it exhibits a different mechanism from that in higher plants. The transformant (T1) was demonstrated to have higher phycobilisomes and lower LHC binding pigments, resulting in a redder color, higher sensitivity to salt stress, smaller in size, and slower growth rate than the wildtype (WT). The photosynthetic performances of T1 and WT showed similar characteristics; however, P700 reduction was slower in T1. Most importantly, T1 could release a high percentage of carpospores in young blades to switch generation during its life cycle, which was rarely seen in WT. The co-suppression of PyLHCI revealed its key roles in light harvesting, stress resistance, and generation alternation (generation switch from gametophytes to sporophytes, and reproduction from asexual to sexual).