*Article* **Expression of Genes Related to Carrageenan Synthesis during Carposporogenesis of the Red Seaweed** *Grateloupia imbricata*

### **Pilar Garcia-Jimenez \*, Sara R. Mantesa and Rafael R. Robaina**

Departamento de Biología, Facultad de Ciencias del Mar, Instituto de Estudios Ambientales y Recursos Naturales, Universidad de Las Palmas de Gran Canaria, E-35017 Las Palmas de Gran Canaria, Spain; saramantesa@gmail.com (S.R.M.); rafael.robaina@ulpgc.es (R.R.R.)

**\*** Correspondence: pilar.garcia@ulpgc.es

Received: 22 July 2020; Accepted: 18 August 2020; Published: 19 August 2020

**Abstract:** Carrageenan, the foremost constituent of extracellular matrix of some rhodophyta, is a galactan backbone with a different number of sulphate groups attached. Variations of degree of sulphation are associated with different types of carrageenans, which vary according to seaweed life cycles, and have consequences for the exploitation of this raw material. In this work, we used three well-recognised stages of development thalli and two stages of cystocarp maturation to analyse genes that encode addition and elimination of sulphate groups to cell-wall galactan of the red seaweed *Grateloupia imbricata*. Expressions of *carbohydrate sulfotransferase* and *galactose-6 sulfurylase* and genes encoding stress proteins such as cytochrome P450 and WD40, were examined. Results showed that transcript expression of *carbohydrate sulfotransferase* occurs at all stage of thalli development. Meanwhile *galactose-6 sulfurylase* expressions displayed different roles, which could be related to a temporal regulation of cystocarp maturation. *Cytochrome P450* and *WD40* are related to the disclosure and maturation of cystocarps of *G. imbricata*. Our conclusion is that differential expression of genes encoding proteins involved in the sulphation and desulphation of galactan backbone is associated with alterations in thalli development and cystocarp maturation in the red seaweed *Grateloupia imbricata*. Exploitation of industry-valued carrageenan will depend on insight into gene mechanisms of red seaweeds.

**Keywords:** carbohydrate sulfotransferase; carrageenan; cytochrome P450; galactose-6 sulfurylase; red alga; reproduction stages; WD 40
