**3. Methylated Ins-derivatives in plant cell and the biotechnological use to increase stress tolerance**

Some plants use Ins as precursor of compatible solutes such as D-ononitol and D-pinitol, which act as osmoprotectants (small molecules that act as osmolytes and help organisms survive in extreme osmotic stress [35]). In halophyte ice plant (*Mesembryanthemum crystallinum*), which is considered highly tolerant to drought, salinity, and cold, Ins is methylated to D-ononitol and subsequently epimerized to D-pinitol [36]. The myo-inositol O-methyl transferase gene (IMT1; EC 2.1.1.40; Figure 1) is transcriptionally induced by osmotic stress, whereas neither transcriptional nor enzyme activities is detectable in ice plants under normal growth condi‐ tions [37, 38]. Despite the positive influence of these metabolites in plant physiology under abiotic stress conditions, there are less available data for these compounds compared with phosphorylated Ins-derivatives.


**†**Enzyme Commission; **\***According to KEGG Database Pathway; − Not observed; Overexp. (Overexpression); **Legend:** HS (high salinity); P (paraquat); PEG (polyethylene glycol); HT (high temperature); OS (oxidative stress); D (drought); DH (dehydration); ABA (ABA hormone); OSM (osmotic stress); F (freezing). **a**. Albeit to a variable extent, overexpres‐ sion of this gene confers salt-tolerance to diverse evolutionary organisms (from prokaryotes to eukaryotes), including crop plants; **b**. Transgenic individuals presenting retention of approximately 40–80% of the photosynthetic competence under analyzed stress condition; **c.** Transgenic individuals retained more chlorophyll and carotenoid by protecting the photosystem II; **d**. Improving seed germination and seedling growth in transgenic individuals under stress conditions; **e**. Expression patterns of various stress responsive genes were enhanced, and the activities of antioxidative enzymes were elevated in transgenic plants; **f**. The transcripts of various stress-responsive genes are increased in ThIPK2 trans‐ genic plants under salt stress condition; **g**. The sense transgenic plants had higher relative water content, better osmotic adjustment, increased photosynthesis rates, lower percentage of ion leakage and less lipid membrane peroxidation, higher grain yield than the wild type; **h**. The 1,3,4-trisphosphate 5/6-kinase is a negative regulator of osmotic stress signaling in tobacco; **i**. The genetic evidence indicating that phosphoinositols mediate ABA and stress signal transduc‐ tion in plants, and their turnover is critical for attenuating ABA and stress signaling; **j**. Salt stress responses, such as increased plasma membrane endocytosis and the intracellular production of ROS, are coordinated by phospholipidregulated signaling pathways; **l**. AtPI4Kγ3 is activated by DNA demethylation and regulates the ROS accumulation induced by high salt treatment or ABA treatment; **m**. ZmPIS regulates the plant response to drought stress through altering membrane lipid composition and increasing ABA synthesis in maize; **n**. AtPAP15 (3-PHYTASE) may modu‐ late AsA levels by controlling the input of myoinositol into this branch of AsA biosynthesis in *Arabidopsis thaliana*. *At*: *A. thaliana; Pc: P. coarctata; Sa: S. alterniflora; Ca: C. arietinum; Th: T. halophile; Zm: Z. mays; Os: O. sativa*; *Nt: N. tabacum; Bn: B. napus; Bj: B. juncea.*

**Table 1.** Transgenic and knockout plant assays available in the literature related to (poly)phosphoinositides and inositol (poly)phosphates. Relevant information: EC number of the enzyme coded by the studied gene, plant donor species, the genetically modified organisms (transformants), the modulation of the studied gene, the analyzed stress condition, the impact on plant tolerance and physiology (additional details, please see the legends).

Sheveleva et al. [39] were one of the first to report the biotechnological potential of methylated Ins-derivatives. In their work, the authors superexpressed O-methyltransferase (IMT1; EC 2.1.1.40; Figure 1) of *Mesembryanthemum crystallinum* in tobacco (*Nicotiana tabacum* cv. SRl). The transgenic plant increased its tolerance to abiotic stresses [drought and high salinity (50–250 mM NaCl)] when compared to the wild control line. An accumulation of methylated inositol D-ononitol in amounts of fresh weight exceeding 35 μmol g-1 in the transformed lines was observed. Besides, the photosynthetic CO2 fixation was less inhibited in those plants during drought and salt stress. Further, transformed plants recovered faster than the wild type after rehydration. In turn, Sengupta et al. [40] observed an increase of the D-pinitol synthesis in a wild-type rice (*Porteresia coarctata*) with halophilic characteristics when subjected to high salt environment (400 mM NaCl). An increment also occurred in both transcriptional and proteo‐ mic level of IMT1, not observable in domesticated rice under the same condition. The authors also reported an increase in the expression of L-myo-inositol 1-phosphate synthase (PcMIPS1; EC 5.5.1.4; Figure 1), along with the expression of IMT1. According to the authors, this suggests that the accumulation of D-pinitol would be a mechanism regulated by salt stress.

**EC† Number Gene origin**

*Bn: B. napus; Bj: B. juncea.*

**(specie)**

88 Abiotic and Biotic Stress in Plants - Recent Advances and Future Perspectives

**Transformant (specie)**

3.1.3.25 *Ca At* Overexp. HS, P, PEG,

2.7.1.140; 2.7.1.151 *Th Bn* Overexp. HS, D, and

2.7.1.149 *At At* Overexp. HS, D, and

**Gene Modulation**

5.5.1.4 *Pc Os and Bj* Overexp. HS Raise [25] a. 5.5.1.4 *Pc Nt* Overexp. HS Raise [21] b. 5.5.1.4 *As At* Overexp. HS Raise [22] c.

2.7.1.140; 2.7.1.151 *At Nt* Overexp. HS and OS Raise [27] e.

**†**Enzyme Commission; **\***According to KEGG Database Pathway; − Not observed; Overexp. (Overexpression); **Legend:** HS (high salinity); P (paraquat); PEG (polyethylene glycol); HT (high temperature); OS (oxidative stress); D (drought); DH (dehydration); ABA (ABA hormone); OSM (osmotic stress); F (freezing). **a**. Albeit to a variable extent, overexpres‐ sion of this gene confers salt-tolerance to diverse evolutionary organisms (from prokaryotes to eukaryotes), including crop plants; **b**. Transgenic individuals presenting retention of approximately 40–80% of the photosynthetic competence under analyzed stress condition; **c.** Transgenic individuals retained more chlorophyll and carotenoid by protecting the photosystem II; **d**. Improving seed germination and seedling growth in transgenic individuals under stress conditions; **e**. Expression patterns of various stress responsive genes were enhanced, and the activities of antioxidative enzymes were elevated in transgenic plants; **f**. The transcripts of various stress-responsive genes are increased in ThIPK2 trans‐ genic plants under salt stress condition; **g**. The sense transgenic plants had higher relative water content, better osmotic adjustment, increased photosynthesis rates, lower percentage of ion leakage and less lipid membrane peroxidation, higher grain yield than the wild type; **h**. The 1,3,4-trisphosphate 5/6-kinase is a negative regulator of osmotic stress signaling in tobacco; **i**. The genetic evidence indicating that phosphoinositols mediate ABA and stress signal transduc‐ tion in plants, and their turnover is critical for attenuating ABA and stress signaling; **j**. Salt stress responses, such as increased plasma membrane endocytosis and the intracellular production of ROS, are coordinated by phospholipidregulated signaling pathways; **l**. AtPI4Kγ3 is activated by DNA demethylation and regulates the ROS accumulation induced by high salt treatment or ABA treatment; **m**. ZmPIS regulates the plant response to drought stress through altering membrane lipid composition and increasing ABA synthesis in maize; **n**. AtPAP15 (3-PHYTASE) may modu‐ late AsA levels by controlling the input of myoinositol into this branch of AsA biosynthesis in *Arabidopsis thaliana*. *At*: *A. thaliana; Pc: P. coarctata; Sa: S. alterniflora; Ca: C. arietinum; Th: T. halophile; Zm: Z. mays; Os: O. sativa*; *Nt: N. tabacum;*

**Table 1.** Transgenic and knockout plant assays available in the literature related to (poly)phosphoinositides and inositol (poly)phosphates. Relevant information: EC number of the enzyme coded by the studied gene, plant donor species, the genetically modified organisms (transformants), the modulation of the studied gene, the analyzed stress

Sheveleva et al. [39] were one of the first to report the biotechnological potential of methylated Ins-derivatives. In their work, the authors superexpressed O-methyltransferase (IMT1; EC

condition, the impact on plant tolerance and physiology (additional details, please see the legends).

3.1.4.11 *Zm Zm* Overexp. D Raise [29] g. 2.7.1.159; 2.7.1.134 *Os Nt* Overexp. HS Decrease [24] h. 3.1.3.57 *At At* Knockout HS, F, and D Decrease [30] i. 2.7.1.137 *At At* Knockout HS Decrease [31] j. 2.7.1.67 *At At* Overexp. HS and ABA Raise [23] l. 2.7.8.11 *Zm Zm* Overexp. D Raise [32] m. 3.1.3.8 *At At* Overexp. HS and OSM Raise [33] n.

**Analysed Condition**

and HT

OS

**Impact on Tolerance**

**Authors Notes**

Raise [26] d.

Raise [28] f.

ABA \*\* [34] <sup>−</sup>

Recently, Zhu et al. [41] used a similar strategy as the one developed by Sheveleva et al. [39] to express in *A. thaliana*, a gene coding IMT1, from *Mesembryanthemum crystallinum*. The transformed plants showed higher growth compared to the wild control line and increased tolerance to cold stress (4°C). This increment in tolerance was attributed to different factors: (1) the electrolyte leakage content in the transgenic plants was significantly lower than that of the wild-type plants after freezing stress, showing less damage to the membranes of those plants; (2) transgenic plants showed lower MDA content than wild-type plants, not only in normal conditions but also after stress; and (3) a higher proline content presented in transgenic lines than in wild type, after application of stress.
