Comparative transcriptome analysis reveals the promoting effects of IAA on biomass production and branching of Gracilariopsis lemaneiformis.

Gracilariopsis lemaneiformis is one of main economical species cultivated seaweed in China. The yield of Gracilaria lemaneiformis was positive related with its rhizoid branching number and length, whereas the regulation on branching and growth of G. lemaneiformis was unclear. IAA was well known to control morphogenesis and growth in land plants. This study aimed to evaluate the roles of IAA on the growth and branch formation of G. lemaneiformis rhizoids. In the present research, IAA can enhance the length of rhizoids, branch rhizoids quantity and elongation to remarkably improved the relative growth rate (RGR) of G. lemaneiformis. The intracellular IAA level increased rapidly exposed to IAA, and then partly conjugated amino acid to form inactive IAA-Asp and IAA-Gly to maintain IAA homeostasis in G. lemaneiformis. To understand the regulatory mechanism of G. lemaneiformis to IAA, we performed transcriptome analysis of branch rhizoids and 2 cm primary rhizoids. IAA could activate the pathways in ABCB auxin transporters, precursor biosynthesis of growth-related hormones and plant hormone signal transduction. IAA promoted the precursors synthesis of CTKs, GAs and BR and activated the ARFs involved in IAA signal transduction, and ARR-A and ARR-B involved in CTKs signal transduction, which further regulate the genes encoding cyclin-dependent kinases, cyclins, tubulin, and cell division cycle involved in cell division process. Meanwhile, carbon fixation, carbohydrate metabolism, energy metabolism, and amino acid biosynthesis and metabolism were also responsive to IAA, revealed that IAA induced to produce more energy and metabolic intermediates for cell growth. Furthermore, the transcriptome results were in general consistent with the changes in physiological parameters associated with photosynthesis and nitrogen assimilation systems. These pathways might coordinate together to promote the growth of G. lemaneiformis in response to IAA. These findings could facilitate our understanding into the molecular mechanisms of increases the rhizoid branch formation and growth of G. lemaneiformis. • IAA enhanced lengt h and branching of rhizoids to promote growth of Gracilaria lemaneiformis. • IAA increased the photosynthetic efficiency and NR, GS activity in G. lemaneiformis. • IAA level increased exposed to IAA and formed IAA conjugates in G. lemaneiformis. • IAA activated IAA and CTKs signal transduction to regulate cell division process. • Carbon fixation, C, N and energy metabolism were responsive to IAA. [ABSTRACT FROM AUTHOR]