Comparative transcriptome analysis of developmental stages of the Limonium bicolor leaf generates insights into salt gland differentiation

Abstract

With the expansion of saline land worldwide, it is essential to establish a model halophyte to study the salt-tolerance mechanism. The salt glands in the epidermis of Limonium bicolor (a recretohalophyte) play a pivotal role in salt tolerance by secreting excess salts from tissues. Despite the importance of salt secretion, nothing is known about the molecular mechanisms of salt gland development. In this study, we applied RNA sequencing to profile early leaf development using five distinct developmental stages, which were quantified by successive collections of the first true leaves of L.bicolor with precise spatial and temporal resolution. Specific gene expression patterns were identified for each developmental stage. In particular, we found that genes controlling salt gland differentiation in L.bicolor may evolve in a trichome formation, which was also confirmed by mutants with increased salt gland densities. Genes involved in the special ultrastructure of salt glands were also elucidated. Twenty-six genes were proposed to participate in salt gland differentiation. Our dataset sheds light on the molecular processes underpinning salt gland development and thus represents a first step towards the bioengineering of active salt-secretion capacity in crops. The salt glands play a pivotal role in salt tolerance of exo-recretohalophytes by secreting excess salts from tissues and nothing is known about the molecular mechanisms of salt gland development. In this study, the deep transcriptomic surveys and qRT-PCR analysis were conducted based on the histological observations of the leaf development in Limonium bicolor. The salt gland was the first differentiated epidermal structure of L. bicolor and differentiated two days earlier than the stomata. A series of key genes were proposed to be involved in salt gland differentiation.