Dealing with extremes: insights into development and operation of salt bladders and glands

Figures & data

Figure 1. Structure of salt-secreting modified trichomes in recretohalophytes. A. A salt bladder complex includes an epidermal bladder cell (EBC) and a stalk cell in C. album (from Zhang et al. (2022) and only EBC in M. crystallinum (from Oh et al. (2015); scalebar: 0.5 mm); B. Salt gland structures include single salt gland in O. coarctata (Koteyeva et al., 2022; n, nucleus; scalebar: 10 µm), bicellular salt gland in Chloris gayana Kunth (Oi et al., 2012; BC, basal cell; BR, base region of basal cell; Ca, cavity; CC, cap cell; Cu, cuticular layer; E, epidermal cell; M, mesophyll cell, n, nucleus; NR, neck region of basal cell; Va, valleculae; arrows: plasmodesmata) and multicellular salt gland in L. bicolor (Yuan et al., 2015; SC, secretory cell; AC, accessory cell; IC, inner cup cell; OC, outer cup cell; CC collection cell; scalebar: 5 µm). Modified from: A - Zhang et al. (2022) and Oh et al. (2015); B – Koteyeva et al. (2022), Oi et al., (2012) and Yuan et al. (2015) with permission from John Wiley and Sons; Springer Nature; and University of Chicago Press.

Table 1. Genes involved in formation of salt bladders or glands in recretohalophytes.

Gene name	Function	Descriptions	Species	Reference
WM28	↑ trichome number in Arabidopsis; ↑ probably EBC development	A putative jasmonate-induced gene	M. crystallinum (Salt bladders)	(Roeurn et al., 2016)
McMYB2		R2R3 MYB transcription factor		(Roeurn et al., 2017)
		HD-ZIP IV transcription factor
McC4HDZ
REBC	↑ EBCs and chloroplasts formation	Encodes a WD40 protein; locates to the nucleus and chloroplasts	C. quinoa (Salt bladders)	(Imamura et al., 2020)
CqTTG1-like1	↑ trichome development	Homologs of TTG1 in Arabidopsis and encode a WD40 protein
CqTTG1-like2
REBC-like1	No effects on EBCs formation when this gene exists only			(Moog et al., 2022)
LbHLH	↑ trichome development; ↓ root hair differentiation in Arabidopsis; ↑ salt gland density and appearance; ↑ salt tolerance of Arabidopsis; ↓ salt tolerance of sea lavender	A bHLH transcription factor but less than 30% sequence similarity with that in Arabidopsis; locates to the nucleus	L. bicolor (Salt glands)	(Wang et al., 2021; Yuan et al., 2022)
LbTTG1		Encodes a WD40-repeat protein with high sequence similarity to TTG1 in Arabidopsis; locates to the nucleus		(Yuan et al., 2019, 2022)
LbSAD2	↑ trichome development; ↓ root hair differentiation in Arabidopsis; ↑ salt tolerance of Arabidopsis	Encodes an importin-β protein		(Xu et al., 2020)
LbMYB48	↑ salt gland development and salt secretion ability; ↑ tolerance of Arabidopsis	R1type MYB transcription factor; locates to the nucleus		(Han et al., 2022)
Lb1G04794	↑ trichome development; ↓ regulate root hair differentiation in Arabidopsis; ↑ salt gland development; ↑ salt tolerance of Arabidopsis	Do not contain transmembrane domain, signal peptide and conserved domain; locates to the nucleus		(Jiao et al., 2022)
LbCPC	↓ salt gland development and density; ↓ trichome number, ↑ root hair number, ↑ salt sensitivity of Arabidopsis	MYB transcription factor; locates to the nucleus		(Zou et al., 2023)

Notes: ↑ and ↓ means positive and negative regulation, respectively.

Figure 2. Maximum likelihood tree of GL2 (A), TTG2 (B) and GL3 (C) proteins from glycophytes and recretohalophytes. Genes in glycophytes and recretohalophytes were marked by solid circle. The percentage of trees in which the associated taxa clustered together is shown next to the branches. The tree is drawn to scale, with branch lengths measured in the number of substitutions per site. Evolutionary analyses were conducted in MEGA X.

Table 2. Homologs of trichome development-related genes in glycophytes and recretohalophytes.

Group	Trichomes or modified trichomes	Organism	Absence or presence of genes
			R2R3-MYB	WD40	bHLH	HD-Zip	WRKY	RBR1	SIM	R3-MYB
			GL1	TTG1	GL3/EGL3	GL2	TTG2			TRY	CPC	ETC1/2/3	TCL1/2
Glycophytes	Trichomes	A. thaliana	+	+	+	+	+	+	+	+	+	+	+
		G. hirsutum	+	+	+	+	+	+	+	+	+	+	+
		A. annua	+	+	+	+	+	+	–	+	+	+	+
		C. sativus	+	+	+	+	+	+	–	+	+	+	+
		S. lycopersicum	+	+	+	+	+	+	–	+	+	+	+
		O. sativa	+	+	+	+	+	+	–	+	+	+	+
Recretohalophytes	Unicellular salt glands	O. coarctata	+	–	+	+	+	+	–	+	+	+	–
	Bicellular salt glands	Z. matrella	+	+	+	+	+	+	–	+	+	+	+
		A. littoralis	+	+	+	+	+	–	–	+	+	+	+
	EBCs	C. quinoa	+	+	+	+	+	+	–	+	+	+	+
	Salt glands or EBCs	G. soja	+	+	+	+	+	+	–	+	+	+	+
	Multicellular salt glands	A. corniculatum	+	+	+	+	+	+	–	+	+	+	+
		A. marina	+	+	+	+	+	+	–	+	+	+	+
		L. bicolor	+	+	+	–	–	+	–	+	+	+	+

Figure 3. Confocal imaging of Na⁺ fluorescence using CoroNa Green AM in salt glands of A. lagopoides under control and 300 mM NaCl for 3 days.

Table 3. Genomes-sequenced of recretohalophytes with salt bladders or salt glands until 2023.

Species	Family	Class	Secreting structure	Assembly level	Available database	References
C. quinoa	Amaranthaceae-Chenopodiaceae	Dicot	EBCs	Scaffold	Index of /genomes/genbank/plant/Chenopodium_quinoa (nih.gov).. .. (NCBI)	(Jarvis et al., 2017; Zou et al., 2017)
M. crystallinum	Aizoaceae	Dicot	EBCs	Chromosome	Contact the authors of the reference	(Shen et al., 2022)
A. marina	Acanthaceae-Avicennioideae	Dicot	Salt glands (multicellular)	Chromosome	https://datadryad.org/stash/dataset/doi:10.5061/dryad.3j9kd51f5. .. .	(Friis et al., 2020; Natarajan et al., 2021)
A. corniculatum	Primulaceae-Myrsinaceae	Dicot	Salt glands (multicellular)	Chromosome	https://ftp.cngb.org/pub/CNSA/data3/CNP0001270/CNS0267886/CNA0017738/.. .. (CNGBdb)	(Feng et al., 2021; Ma et al., 2021)
G. uralensis	Fabaceae-Papilionoideae	Dicot	Salt glands (multicellular)	Scaffold	http://ngs-data-archive.psc.riken.jp/Gur-genome/download.pl.. .. (Dead link)	(Mochida et al., 2017)
G. soja	Fabaceae-Papilionoideae	Dicot	Salt glands or EBCs	Chromosome	http://www.wildsoydb.org/Gsoja_W05/; https://soybase.org/data/public/Glycine_soja/. ...	(Valliyodan et al., 2019; Xie et al., 2019)
L. bicolor	Plumbaginaceae	Dicot	Salt glands (multicellular)	Chromosome	Index of /genomes/genbank/plant/Limonium_bicolor (nih.gov).. .. (only assembly available from NCBI)	(Yuan et al., 2022)
A. littoralis	Poaceae-Chloridoideae	Monocot	Salt glands (bicellular)	Contig	https://doi.ipk-gatersleben.de/DOI/ac423f10-971e-481e-bcab-6ac261e27f5c/15d455e1-da91-4e78-82d8-7c7607cb05b9/2/1847940088.. ..	(Hashemi-Petroudi et al., 2022)
Z. matrella	Poaceae-Chloridoideae	Monocot	Salt glands (bicellular)	Scaffold	http://zoysia.kazusa.or.jp/.. ..	(Tanaka et al., 2016)
Z. japonica	Poaceae-Chloridoideae	Monocot	Salt glands (bicellular)	Scaffold		(Tanaka et al., 2016)
Z. pacifica	Poaceae-Chloridoideae	Monocot	Salt glands (bicellular)	Scaffold		(Tanaka et al., 2016)
O. coarctata	Poaceae-Oryzoideae	Monocot	Salt glands (unicellular)	Scaffold	http://ccbb.jnu.ac.in/ory-coar/.. ..	(Bansal et al., 2021)

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