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Lectin receptor-like kinases (LecRLKs) are class of membrane proteins found in higher plants that are involved in diverse functions ranging from plant growth and development to stress tolerance. The basic structure of LecRLK protein comprises of a lectin and a kinase domain, which are interconnected by transmembrane region. Here we have identified LecRLKs from Arabidopsis and rice and studied these proteins on the basis of their expression profile and phylogenies. We were able to identify 32 G-type, 42 L-type and 1 C-type LecRLKs from Arabidopsis and 72 L-type, 100 G-type and 1 C-type LecRLKs from rice on the basis of their annotation and presence of lectin as well kinase domains. The whole family is rather intron-less. We have sub-grouped the gene family on the basis of their phylogram. Although on the basis of sequence the members of each group are closely associated but their functions vary to a great extent. The interacting partners and coexpression data of the genes revealed the importance of gene family in physiology and stress related responses. An in-depth analysis on gene-expression suggested clear demarcation in roles assigned to each gene. To gain additional knowledge about the LecRLK gene family, we searched for previously unreported motifs and checked their importance structurally on the basis of homology modelling. The analysis revealed that the gene family has important roles in diverse functions in plants, both in the developmental stages and in stress conditions. This study thus opens the possibility to explore the roles that LecRLKs might play in life of a plant.

Lectin receptor-like kinases (LecRLKs) are members of RLK family composed of lectin-like extracellular recognition domain, transmembrane domain and cytoplasmic kinase domain. LecRLKs are plasma membrane proteins believed to be involved in signal transduction. However, most of the members of the protein family even in plants have not been functionally well characterized. Herein, we show that Pisum sativum LecRLK (PsLecRLK) localized in plasma membrane systems and/or other regions of the cell and its transcript upregulated under salinity stress. Overexpression of PsLecRLK in transgenic tobacco plants confers salinity stress tolerance by alleviating both the ionic as well the osmotic component of salinity stress. The transgenic plants show better tissue compartmentalization of Na(+) and higher ROS scavenging activity which probably results in lower membrane damage, improved growth and yield maintenance even under salinity stress. Also, expression of several genes involved in cellular homeostasis is perturbed by PsLecRLK overexpression. Alleviation of osmotic and ionic components of salinity stress along with reduced oxidative damage and upregulation of stress-responsive genes in transgenic plants under salinity stress conditions could be possible mechanism facilitating enhanced stress tolerance. This study presents PsLecRLK as a promising candidate for crop improvement and also opens up new avenue to investigate its signalling pathway.

Trehalose 6-phosphate (Tre6P), a sucrose signaling metabolite, inhibits transitory starch breakdown in Arabidopsis (Arabidopsis thaliana) leaves and potentially links starch turnover to leaf sucrose status and demand from sink organs (Plant Physiology, 163, 2013, 1142. To investigate this relationship further, we compared diel patterns of starch turnover in ethanol-inducible Tre6P synthase (iTPS) lines, which have high Tre6P and low sucrose after induction, with those in sweet11;12 sucrose export mutants, which accumulate sucrose in their leaves and were predicted to have high Tre6P. Short-term changes in irradiance were used to investigate whether the strength of inhibition by Tre6P depends on starch levels. sweet11;12 mutants had twofold higher levels of Tre6P and restricted starch mobilization. The relationship between Tre6P and starch mobilization was recapitulated in iTPS lines, pointing to a dominant role for Tre6P in feedback regulation of starch mobilization. Tre6P restricted mobilization across a wide range of conditions. However, there was no correlation between the level of Tre6P and the absolute rate of starch mobilization.Rather, Tre6P depressed the rate of mobilization below that required to exhaust starch at dawn, leading to incomplete use of starch. It is discussed how Tre6P interacts with the clock to set the rate of starch mobilization. K E Y W O R D SArabidopsis, circadian clock, diel, starch, trehalose 6-phosphate | INTRODUCTIONPlants use light energy to drive photosynthetic carbon (C) gain, metabolism, and growth, but at night depend on C reserves accumulated in previous light periods. In many species, including Arabidopsis, foliar starch is the major C reserve (Smith & Stitt, 2007). Diel regulation of starch turnover may depend on the conditions (Paul & Foyer, 2001). In source-limited plants, C is in short supply and it is crucial to manage C reserves to insure rapid investment in growth while avoiding C starvation at night (Scialdone and Howard, 2015;Smith & Stitt, 2007;Stitt & Zeeman, 2012). In sink-limited conditions, C regulation of metabolism and growth is relaxed (Baerenfaller et al., 2015;Sulpice et al., 2014) and starch often accumulates in leaves and other parts of the plant. This incomplete utilization of starch may be at least partly due to feedback inhibition of starch mobilization by the sucrose signal trehalose 6-phosphate (Figueroa Lunn, Delorge, Figueroa, Van Dijck, & Stitt, 2014;Martins et al., 2013). The following experiments provide further evidence that Tre6P plays a key role in the feedback regulation of starch mobilization. In particular, we ask whether feedback inhibition by Tre6P is minimized to allow full use of starch in conditions where C is in short supply, but operates effectively when C is in excess.When Arabidopsis plants grow in conditions where less C is available per 24 hr cycle, they accumulate a larger proportion of their fixed C to starch in the daytime and slow down mobilization of starch during the night, compared to plants growing with a larg...

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