**Acknowledgements**

*Legume Crops - Prospects, Production and Uses*

FD48 that modules the expression of some genes involved in the synthesis of auxins improving root elongation in rice [98] and *Pseudomonas aeruginosa* and *Burkholderia gladioli* that reduced the expression of *CAT*, *GR*, *GPOX*, *APOX*, and *GST* genes in the presence of Cd stress in *Lycopersicon esculentum* plants modulating their antioxidative response [98]. *P. aeruginosa* and *Bacillus gladioli* also elevated the expression of phenolic compound, osmolytes, and molecular weight organic acid (citric acid, malic acid, fumaric acid, and succinic acid) genes, decreasing the physiological

A global transcriptomic analysis was carried in inoculated *Medicago truncatula* plants grown in the presence of arsenic and inoculated with an arsenic-resistant rhizobial strain. The results showed the overexpression of some defense genes in the inoculated plants (sulfur metabolism, several enzymes of the phytochelatins synthesis pathway, proline, heat shock proteins, and several transcription factors). Besides, secondary metabolism, isoflavonoids and phenylpropanoids, were activated. In contrast, the genes of nodulation were downregulated, particularly those

Under drought environments, *P. putida* MTCC5279 modulates the stress in plants of *Cicer arietinum* by the overexpression of *ACO* and *ACS* (involved in the synthesis of ethylene); *PR1* (synthesis of salicylic acid); *MYC2* (synthesis of jasmonate); *SOD, CAT, APX*, and *GST* (genes that codify the antioxidative enzymes in plants); *DREB1A* (response element to dehydration); *LEA* and *DHN* (dehydrins); and *NAC1* (transcription factors expressed under abiotic stress) genes [101]. In plants of sorghum inoculated with rhizobacterial endophytes, proline (a crucial molecule of maintaining the cellular functions under drought) accumulation was higher than in the noninoculated plants because bacteria induce the overexpression of *sbP5CS2* (pyrroline-5-carboxylate synthase 2) and *sbP5CS1* (pyrroline-5-carboxylate synthase 1) genes under drought stress [102]. This fact also was demonstrated in inoculated chickpea plants, where proline was accumulated by plants under

drought conditions besides histidine, citrulline, and threonine [103].

Finally, the molecular mechanisms for plant alleviation in salt stress by bacteria are also reported by some authors. A transcriptome of rice plants inoculated with *Bacillus amyloliquefaciens* SN13 showed that the bacterial inoculation alters gene expression under salt stress. For example, genes of phytohormones, flavonoids, or photosynthesis are found in higher number in inoculated plants [104]. Other example is the inoculation of wheat with *Dietzia natrolimnaea* that causes an overexpression of genes involved in the ABA signaling cascade and in the salt sensitive

Recently, some authors have studied the miRNAs induced by PGPR as a possibility to regulate the stress in plants [106, 107]. miRNAs are RNA molecules of 20–24 nucleotides that do not codify proteins, and they get bound to mRNA or any transcriptional factor, regulating the expression of the target gene. However, the only study about miRNAs was performed in chickpea plants under drought stress, where plants were inoculated with *Pseudomonas putida* RA, and this inoculation improves plants adaptation to drought conditions through the regulations of

One of the main problems of the rapid increase in the world's population lies in the challenge of having the necessary food for global supply, but the climate change and the pollution decrease the number of the agricultural soil, so a possible solution would be to encourage more widespread use of PGPB. The evidence that PGPR

damage of *Solanum lycopersicum* plants under Cd toxicity [98].

involved in the early stages of the interaction [99, 100].

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pathway among others [105].

miRNA expression [108].

**4. Conclusions and future perspectives**

This research was funded by Junta de Andalucia (Spain) under FEDER 2020/00000092 project.
