** U.S. bank Investar Holding's ISTR.O shares jump as much as 12.3%; last up 10% at $18.69

** Piper Sandler upgrades ISTR to "overweight" from "neutral"; raises PT to $22 from $21, a 30% upside to stock's last close

** Brokerage says ISTR earlier this week delivered strong Q1 results, supported by the bank's execution on deposit management

** Says ISTR trading at a discount to tangible book value seems excessive given the bank's improving profitability profile, which could re-attract attention as earnings power improves

** Brokerage also doesn't expect any sort of meaningful uptick in credit costs at ISTR and believes the bank remains well-reserved for any surprises

** All three brokerages covering the stock rate it "buy" or higher; median PT $22.50 — data compiled by LSEG

** As of last close, ISTR shares down 22.7% YTD

(Reporting by Arasu Kannagi Basil in Bengaluru)

((ArasuKannagi.Basil@thomsonreuters.com))